Obviously you need to have some high level idea of what's going on in the world around the players, and where you are heading with the story, but in an ongoing game at some point players will be players and will head off in a different direction to what you planned.

How far ahead should you be planning to minimise or eliminate being caught off guard, but also try to minimise the amount of 'wasted content' you come up with but never gets used?

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    \$\begingroup\$ I have found that no matter how hard I prep, the party always finds a way to do things and go places I hadn't prepped for. \$\endgroup\$
    – BBlake
    Commented Oct 30, 2010 at 21:43
  • 1
    \$\begingroup\$ Also some good advice for new gms (though not about prep) here: Your friend wants to learn the ways of the Dungeon Master, what do you do? \$\endgroup\$
    – yhw42
    Commented Jan 27, 2011 at 0:52
  • 1
    \$\begingroup\$ I'm voting to close this as too broad, as it's a very system-dependent matter. How much material is needed, and what and how much should be prepared, vary system to system. \$\endgroup\$ Commented Jun 6, 2016 at 11:53
  • 2
    \$\begingroup\$ @doppelgreener I agree that it's system-dependent, but the answers given are providing useful ways to figure it out depending on your system and context, and so I think calling it too broad is doing a disservice to our users' expertise. \$\endgroup\$
    – BESW
    Commented Jun 6, 2016 at 11:55
  • \$\begingroup\$ Always a little more than what you expect, but also always a little less than what you think. \$\endgroup\$
    – Zibbobz
    Commented Apr 10 at 16:29

18 Answers 18


I've centred on using an "Onion topology" for my campaign preparation. I also use a technique, both for campaign and adventure site preparation, whose name (not concept) I've borrowed from the crowd at Dream Pod 9 called "The Y-Cubed Law".

Onion Topology

One mistake I used to make all the time was lavishing waaaaaaaaaaaaaaaaay too much detail on things the players were never likely to find out and, thereby, rob my players of attention to details they were going to be facing constantly in the course of ordinary play from day one. (I blame I.C.E.'s old Campaign Law supplement for this since its step-by-step instructions started with the geography of a whole world including plate tectonics.) The cure, I later found, through much bitter experience, was to stop doing top-down design of my campaign and instead work on it from the bottom up. I later termed this "onion topology".

In onion topology you imagine your campaign world's information is arranged in layers like an onion. First you sketch out a whole onion in very rough detail – this would be things like gods, major continents/nations/whatever-suits-the-scope and other extremely broad-brushed details like that. You then move down to the core of the onion which is where the players are. That core is the immediate environs of where the players will start. In a typical pseudo-European feudal setting (which I will continue using as the example) it could be a single fief with attendant keep, village, outlying manor houses, etc. This you give in detail. You make plans for the keep and the manor houses. You make a map of the village. You place it somewhere in your "whole onion view" and draw up the local terrain according to the rough geography you have already put in place. You populate it with key NPCs (right down to the stats if this is important to your game). You find opportunities for plots via these NPCs. (Reading Georg Polti's The Thirty-Six Dramatic Situations is very helpful here!) You situate any typical adventure sites you want to use in the immediate future: haunted keeps, caves of despair, etc. Then, when everything is ready for your players ...

... you continue planning. Because players never do what you expect them to do. So you fill out the next layer of the onion to nearly the same levels of detail. Maybe you drop some of the finer details like minor NPCs, but you really need to detail one layer of information removed like the overlord's own fief, surrounding subinfeudated neighbours, etc. – anything, in brief, that the players might go to visit on a tangent.

Now you're ready to play. You have enough of a broad-picture view that your campaign isn't completely ad-hoc. You have many details for a smallish area in which you can situate your immediate-term needs for adventures and you have details for a larger area into which your players may suddenly sidetrack so you're not caught with your pants down. From here on in your campaign planning work is easy. Run your adventures. While you're doing that add little details to the next layer out until either your players branch out into it themselves or you're ready to branch out. As soon as they do, you start work on the next layer of the onion, always keeping your campaign details planning one layer removed from where the players currently wander around. This way you have the benefits of planning a campaign (especially the consistency) without the burn-out and the wasted effort. When your campaign finishes your detailed campaign notes will be a patchwork quilt of details and sketchy stuff, but your players will never know. To their eyes you'll have had this wonderfully huge and gloriously detailed campaign that they never reached the boundaries of.

The Y-Cubed Law

Hand in hand with the onion topology I used, since the early '80s, a technique I later grew to call "The Y-Cubed Law" courtesy of the boys at Dream Pod 9. Where the onion topology gives players the illusion of campaign breadth, the Y-cubed law gives the players the illusion of campaign depth.

What I found tending to happen both in my campaigns and others' was that in a bid to bring a place to life people would put in all sorts of interesting local quirks. For example: "In the village of Hothentot the temple bells ring once every ten days at 37 minutes past noon." Or: "In the land-locked city of Kamesh, right in the central square, there is an enormous, 1:1 scale statue of a whale." These are harmless little details of no meaning or merit; just flavour text, really. But ... players will always arrow in on these details and start asking questions. "Why does a land-locked country have a statue of a whale? How would they even know what a whale looks like?" ... and so on ad nauseum. As a player I always found the GMs floundering and looking, frankly, a little stupid as they get blind-sided by such questions and as a GM I floundered and felt, frankly, a little stupid when I got blind-sided.

Enter the Y-cubed law.

In the Y-cubed law, any time you introduce a detail into your setting (or, at its most extreme, into NPCs) you ask yourself the question "Why?" three successive times like this:

  • Q: Why does Hothentot ring its bells once every ten days at 12:37? A: They are celebrating the defeat of a horde of bandits.
  • Q: Why ten days? A: The bandits were defeated by ten doughty adventurers.
  • Q: Why 12:37? A: The time represents the ratio of defenders (ten adventurers plus two hardy locals) and the number of bandits they killed.

There. Now a piece of local colour has something that will stand up to a bit of casual curiosity. It also happens to provide some ideas for possible future adventures. (Where are the adventurers now that the villagers have the wherewithal to actually properly pay them? Were there any surviving bandits who'll come back for revenge?) The total time to ask and answer the Y-cubed can be, after some practice, thirty seconds or so for each detail and yet that minimal time and effort not only gives the illusion of depth but also gives the GM plot seeds that he can use in the future, thus saving time overall.

  • 1
    \$\begingroup\$ Like thee Y-cubed approach. Interestingly enough there is a similar approach in IT consulting to investigate so called 'wicked problems'... :) \$\endgroup\$
    – fgysin
    Commented Mar 8, 2013 at 13:28
  • \$\begingroup\$ So you're saying world building...is like Ogres? \$\endgroup\$
    – Zibbobz
    Commented Apr 10 at 16:31

If the prepping is fun, then keep doing it. If it stops being so much fun, you've done enough (or too much) and need to quit. I don't believe there's a time limit or a ratio or any kind of formula you can use. Do as much prep work as you enjoy, and don't keep going once you stop enjoying it, even if you feel underprepared. You're not. GMing is a mind trick - as long as the players feel like you're ready for them, you are ready for them.

I also recommend a couple of useful articles on game prep and adventure design. Doc Rotwang has a great concept called the Adventure Funnel, and Justin Alexander has a good article called Don't Prep Plots. Check 'em both out.

  • 1
    \$\begingroup\$ +1 For the Adventure Funnel. Not only does a dozen minutes brainstorming give me an entire session's worth of material, but as often as not I then surprise myself with what happens. \$\endgroup\$ Commented Oct 27, 2010 at 15:15
  • 2
    \$\begingroup\$ Yeah, man, that Doc Rotwang guy is like Sonny Crockett AND The Fonz. \$\endgroup\$
    – Dr Rotwang
    Commented Oct 29, 2010 at 3:39
  • 1
    \$\begingroup\$ +1 for Don't Prep Plots. For me that's the last word in adventure prep. \$\endgroup\$
    – cr0m
    Commented Jul 24, 2014 at 23:46

Here's how I do it: I make notes about stuff as it comes to me, until I think to myself,

"Screw it, I can fake the rest."

Sounds almost like a non-answer, I know. But it really is how I do it. I've found that the stuff that gets made up on the spot is livelier and more unexpected than what I plan and draft and double-check, so...I mean, why sweat it?

You must waste your Buddha, my friend.

  • 2
    \$\begingroup\$ +1 Very much so; I have had excellent sessions where my prep was about three lines on a post-it note, like "Visit village. Horror there. Sky raiders allies?" Made the rest up as it went along. \$\endgroup\$
    – Rob
    Commented Jul 24, 2014 at 16:07

After 32 years I still am not as prepared as I would like. That said, here is what I do to not be totally inept at game mastering a session of any game I run.

** The answer below are predicated on the idea that you already know the rules of the game your are GM'ing, and some amount of the world information around the group is already established.

Focus on 3 areas when preparing: Yourself, Your players, the session. In each of these areas are the things I do to handle the unknowns and variables that a party throw into each session.

Yourself: This takes about 5 minutes. Think about how your run your game. Most GM's do not take time to think about themselves in relationship to the game. This is probably the most beneficial thing you can do.

  • What did you do well last time - do that more.
  • What did you do poorly last time - make notes on the issues and what you want to do to correct them.
  • Pick one thing you want to do better. Write it down and make sure you can see it during the game

Your Players: This takes about 15 minutes. Think how the players have responded to the last game session. Not their characters but the actual people. Were they bored, excited, apathetic or something else? What was their style of play, lots of dice rolling or very little dice rolling. Rules quibbling? Laughter? Write it down and focus on enhancing those things that you think are good. This will help you identify and focus and on the reasons you and your group get together and game. Sometimes the reason players throw a monkey wrench into the works is because they crave something other than what is currently happening. Over time, your sessions should be more fun and memorable.

The Session: This take the largest amount of time, usually about 2 hours for each hour of play.

  • Scenario Prep: What are the characters supposed to do for this session?
    This will be as detailed or sketchy as you are comfortable with. Things like locations, NPCs, encounters, puzzles, geography, politics and everything that you normally think about when running a session. Here you will prepare notes, outlines and reference data about the session details. The level of detail is up to you. Some GM's are great at improv, some are not, and some are in the middle. Take what you got from thinking about yourself and apply it here while preparing.
  • Plan your improv. Actually go out and rehearse what the bad guys say or do! Jot down a quick note about how the bad guys feel about the characters and how they might react if they are winning or losing. It will be harder for the players to gum up the works with a bad guy/NPC if you already know what how they will respond.
  • Characters - Prepare a quick cheat sheet of character stats and information that is just for your eyes. Make it small and relevant. Stop asking the players what their stats are, have it in front of you. This will speed up your game and leave less time for players to think of something else they might want to do.
  • Plan The Ending. This take 10 minutes. Make sure you know what the bad guys and the NPCs will do after the party succeeds or fails. This will push your thinking into the next session and begin to give the world around the characters a sort of life outside what they are doing.
  • Plot hooks - Finally take 5 minutes and rethink through scenario and come up with at least one plot hook that can propel the group forward or in a new direction. If the party does this alot then jump on it and make it something you have a better level of control over. If over time the party has 10 or 15 plot hooks you have given them they will begin choosing which to do and which to ignore. The more you do this the more hooks you will come up with. Write them on 3x5 cards and have them ready to hand to the characters as reminders of what options they have. This keeps them focused on the story.

How far do you plan ahead? This depends on how good you are at improv, how predictable the group is, and how well you know the world story the group is in. If you do not know the story well then you should be planning out a long way. If the party is unpredictable then you should be more sketchy in planning and have multiple options, (or really good a railroading the story line). Your improv skills also have a bearing on this.

In short game prep is a very personal thing. These are some solid steps that you can do, but always keep in mind the type of game system, type of group play, and your GM ability. If you do this you will be "surprised" a lot less and have a lot more fun.


There's a lot of good answers about session prep here, but nobody's addressed campaign prep, so I'll try:

For your first session of a new campaign, you need about twice as much prep time as normal. This should usually be spent on characters and events that might be met early in the campaign, and might carry over through the first few sessions. And crucially, be prepared to throw half of it away after your first session. A new world always needs some learn-as-you-go; after the first couple of games you'll have a much better idea what does/doesn't work.

The better I know the world and party, the less prep I need. The more detailed the research, the more prep I need. My long-running Werewolf game has been almost prep-free for about 4 years; I know the world and party so well my prep can be a few lines of notes on what the major NPCs are doing right now... and where the party might have to go to stop them. Until I started doing a series of adventures set in flashback in ancient history (via ancestor-spirits); for this arc I'm running about 3 hrs prep (mostly research and new NPC creation) for every 1 hr play time.

Signs you haven't done enough:

  • You have no idea who/what/which group is in charge in the area the players are in.
  • You don't have future plans (or stats) for the interesting NPC that you improvised last week when the player's did something unexpected.
  • You've got less detail on the lead antagonist than the players do for their characters.
  • This session the PCs will be somewhere new with different characters to meet, but you've only done your usual amount of prep. (New locations with completely new NPCs usually need a lot more prep time than familiar situations. Not only do you need to make the new environment feel as real as the old one, you need more flexibility, as you won't have established NPCs around to fall back on when the players go off-plan and you need to improvise.)
  • You have all the clues to the murder mystery, and the skill checks needed to find them, but you don't know what the fallback plan is if the PCs miss a key clue. (They always miss a key clue. So make sure there's another way to find it or do without it.)

Signs you've done too much:

  • You've invented monster stats for a new species that you don't know if you'll use.
  • You've spent longer on an NPC that you're only using for one session than a player did on his character.
  • You have detailed sketches/maps of anything that the players might not ever see.

Signs that you've done too much prep of one kind, and not enough of another:

  • You have a very detailed map of a dungeon/spaceship/forest, but only a one-line note on why the players will be visiting it.
  • You have invented general stats for a whole new species, but there's only one character of that species, and he only has one function in the plot.
  • You have a detailed marketplace scene, but no idea what kind of people shop there.

(All of this latter category are also warning signs that you're telling your story too much, and involving the players too little.)

Also, campaign prep builds with time. My favourite trick (developed during a Star Wars campaign years ago): Get one - you should only need one every 10 adventures or so - sheet of blank paper. Whenever you realise that you're going to need a major event later in the campaign, immediately scribble a couple of minor events that help introduce the concepts on the sheet. Whenever doing session prep, glance at the sheet, grab a couple of ideas, prep them (take no more than a few minutes; this is early-broad-strokes stuff), and cross them off.

Example: I realise the campaign finale will involve the Evil Overlord invading the Gnome Nation of Leafiness. I scribble 'Leafy gnome traders at market' and 'later: Leafy military buildup. Next time there's a market I remember to throw in the traders, thereby introducing the Leafy nation and the gnome race as part of something I was doing anyway. In a later session I throw in a gnome soldier recalled from leave early. The incidental roleplay with these guys is bound to spark ideas about the Leafies that will save a lot of making-things-up-from-scratch time when I prep the finale. And I get to introduce the concepts I'll need unobtrusively and well in advance.


Fundamentally, the only way to know you've the right prep level is that all of the following are true:

  • you had sufficient material for your session
  • you had no serious concerns that your players would go places you weren't ready for
  • you weren't spending time you needed for other life activities on game prep
  • your players were not overwhelmed by your material
  • your players didn't seem to wonder if you had prepared.
  • you had fun¹
  • your players had fun¹

As long as those all are true, you're doing it right.

Some games do need more prep than others. I found BTVS rewards the 1:1 prep:play ratio I was spending with a game that felt REALLY like playing the TV series. Judge Dredd, I need maybe 1 hour before campaign, to wit, a sector map and some notes, and 20 min per 4 hour game session on rolling up NPC's. And running Houses of the Blooded, my players are spending more prep time; I spent an hour on the campaign, so far, total, for 12+ sessions...

¹: Mind you, what constitutes fun may vary... Some people like gripping angst; others enjoy epic escapism, and others still want to walk the boardgame side... so long as everyone is getting what they consider fun, don't worry about it.


It's definitely a learned skill and it will vary from GM to GM and even from game to game. If you're comfortable with improvising you may not need as much preparation as someone who can't wing it. However if your players never want to venture off the rails, you may never have to improvise for them.

This is a bit of a tangent, but I think it's relevant. When I first started GMing I spent a lot of time on maps, both world and dungeon varieties. I think I did it because I liked the excuse to do something artistic. The problem was that, for my style of GMing, the map translated to negligible play time. If I spent 4-5 hours on a map, I'd be lucky to get the PCs to look at it for a whole minute. They just weren't interested in the details. All they wanted out of the map was what lay between their current location and their destination. I could have come up with that on the fly. "You're going north for 100 miles? Mountains, then forest."

I had a similar experience with dungeons, but it took me a little longer to realize. I stopped drawing them in detail almost immediately because the players never got to see the detailed map. They only ever saw the transcribed version as I drew it out for them. But, as anyone who has copied from grid paper to battle map knows, it's really easy to screw up the details. A corridor that was 10 squares long becomes 9 and then you have to erase it or fudge it. At some point I realized that all those distances were arbitrary. There was little basis for that distance when I created it, so why does it matter that I stick to it so strictly on the copy? Eventually I just stopped mapping. Instead, I write out a list of hazards in the dungeon and deploy them as necessary. I'll draw out individual rooms if they have interesting terrain. But most of my dungeon simply reads "skeleton fight, lava trap, locked door, chess puzzle, zombie fight, magically greased ladder, etc."

On the other hand, when I started GMing I wanted to improvise all my speech. This worked for NPCs, but not so well for description. I'm too quiet of a person to bother describing the stonework and tapestries in the castle. The details would be in my head, but they wouldn't come out unless the players asked for them. For these details to emerge, I had to force myself to prep them. Any time I have to visually describe a scene, that paragraph gets written ahead of time.

So yeah, prep methods vary from person to person. I aim to have enough game planned that even if the PCs nod and smile their way past the NPCs, making no attempts to direct the game session, I have enough prepared that I won't run short at the end of the night. Usually this works out to one page of notes per hour of play time, although if I have a lot of visual description I need more pages. If I think a session is going to run short, I throw in some fights. They're easy to write and I can set them up automatically without thinking about it.

Finally, I only prep one session in advance. Less wasted material if the players go in a direction I didn't anticipate. I have vague notes for what else is going to happen. And I keep track of major NPCs, even when they're off screen. But for the most part, my notes just cover what the players will do.

  • \$\begingroup\$ +1 for mentioning writing up descriptions of scenes in advance. Personally, rather than worrying about the quality of my prose, I write four dot points about locations: Threats, resources, novelties, and exits. I don't worry about the quality of my prose or pure set dressing, since I can make those up on the fly. Somehow, every time I try and describe the place I see in my head without having a written description I end up forgetting the exits - and that can quickly become awkward. \$\endgroup\$
    – GMJoe
    Commented Jan 18, 2012 at 7:00

Well, there's no substitute for experience. In my current campaign, I initially prepped too much, but after a couple sessions it became clear that the players would on average get through X amount of stuff in 5 hours.

The answer varies too much by game system, by player group, and by GM style for too much in the way of objective metrics to make sense - I'd say "prep a lot for game one, and then if you have leftover, use it in game two, and game by game determine what the right amount is."

I generally do a big prep session before each major leg of a campaign, and have a big 10-page Word doc campaign bible to draw from. Then for each session, I usually am piecing together various prefab adventures but changing them and spinning them to fit my ends. So I end up with a 2-3 page Word doc of my own notes, whatever materials I'm using, and then NPC sheets or handouts or whatever the session calls for.

As a benchmark, I spend at least one evening (4 hrs) prepping for a 4 hour session. It can be more if I have to, say, create a bunch of high level D&D NPCs, but that's about the size of it. If I am creating everything from scratch, I might have to do a 2:1 time prep (I spend 8 hours for a 4 hour session). You can cut it leaner (1:2) if you are purely running out of an adventure and not putting your own spin on it much, but I don't do that.


Ask them at the end of the D&D session where they want to go next session, so that you know what to prepare.

If they change their minds at the start of the next session, be up front that you didn't prepare for them to wander into a completely different dungeon.

  • \$\begingroup\$ This is definitely my preferred option. My players are used to the idea that if they can give me some idea where they're planning to go, they'll get much more detailed, self-consistent and enjoyable playing than if they thrash around off-piste on the day. It doesn't stop them leaving the menu any time they decide it's appropriate - they're always in control of their own actions - but it does give us some common idea, which definitely helps with the "big story" elements. \$\endgroup\$
    – MadHatter
    Commented Jan 27, 2011 at 14:24
  • \$\begingroup\$ +1, definitely get the PCs help in your prep work. I play in a Vampire game (one of the many my group kinda-sorta plays from time to time), and in the last 10 years, the Storyteller has only introduced 1 plot device. All the plot of the last 10 years has been us saying, "Before we put this down for a while, I want to do [action]". Almost always fills a session or 2. \$\endgroup\$
    – Pulsehead
    Commented Jan 27, 2011 at 16:43

I was DMing since I was 12 and I turned 35 this week, one important thing I learned is that you are never enough prepared, this is the funny part of being a DM.

The background of each PC in the whole world context is the most important, it's this that outline each session, it happens to me to DMing while walking on the street with a friend, or trough SMSs, e-mails, chat, post cards and whatever I can use.

The rest it's just about details...

So the best things to do is to know what is happening in the world and to prepare just some details, that I call tools.

My personal list is:

  • World, kingdom, News of the day and weather conditions, I keep a journal and I use it while DMing.
  • Any purpose dungeon, maze, combat scenarios maps.
  • Any purpose NPC with a couple of different backgrounds each.
  • Any purpose traps, treasure, special objects.
  • Some funny, dangerous, tender monster for some smart encounter.
  • Any purpose objects and artifacts.

One trick, I make maps with a pen and I use a pencil to write down notes, objects, monsters and so forth, when I need a new map quite fast, I take any maps in my pile, turn it in another way, I put a blank paper on it and I copy the map, a bit of pencil here an there and it's done.

For NPC I use the same trick.

Take notes while DMing, a scenario that you use with one PC group can be used, a bit adapted, with another group, or some years after with the same group (just changing details).

  • \$\begingroup\$ What exactly is a "tender monster"? I'm imagining some kind of cuddly giant bunny devouring whole cities... \$\endgroup\$
    – Joe
    Commented Oct 26, 2011 at 17:34
  • \$\begingroup\$ Yes, you are not far... Pink fur, blue polka dots ... :-) \$\endgroup\$
    – tmow
    Commented Nov 3, 2011 at 23:37

One of my friends who GMed had a rough rule of "spend as much time preparing the game as the players, combined, spend on their characters."

I've found that rule of thumb to be mostly worthwhile, occasionally quite horribly over-prepping for certain games. The time spent on characters indicates how much investement they have in the characters and includes them talking about, writing about, or thinking about the characters. (mechanics versus flavour doesn't matter, as this is a measure of attention.)

Prepping, of course, depends on game. I first decide on which methodology I want to use, be it a 5 room dungeon, or just creating NPCs, motivations, and a location. I never plan out possible actions by the PCs, and I rely quite a lot on improvisational details, planning out whatever framework is necessary.

Overprepping is functionally creating fiction for yourself and not for your players. If you find yourself creating "things" (environments, scenes, etc..) that the players are not expected to interact with, then you've overprepped.


I plan one session ahead. Very little wasted effort that way.

I plan NPCs a bit farther. I like coming up with willful NPCs who will do things regardless of the presence of the PCs. Simulating them can take some time, but I really enjoy watching ripples of their machinations touch the PCs. It's one of those things that improves the game in unexpected ways as the players realize that the world around them is moving.

I do a fair bit of setting research in advance. Were I to make my own setting I'd want to write out most of it far in advance as well. Having background knowledge is helpful. It makes your NPCs seem like they live in a world rather than a fishbowl when they can refer to people and events from outside their own section of the world. I also find that a good setting helps jumpstart ideas. If I really like the Purple Dragon Knights and want to use them, but my players are nowhere near Cormyr, now I've got to come up with a reason why the PDK's are marching on Chessenta.

Setting research is easier than planning for me. I can sit down and read a book for 30 minutes whenever I get a chance. I can't always summon my muse or banish my writers block. Because reading a setting is passive I can get a lot of it done without putting much effort into it.

-edit to add-

A big part of learning to GM is learning what to prep and what not to prep. I'm pretty good at talking, so I don't like writing out big speeches. Just an outline and a couple key sentences. If I do write out a big speech, it ends up detracting from the game's interactivity. However, because I'm decent at speaking through NPCs I assumed I should never write out things to say in advance. It turns out I'm not good at description. I just don't bother with the little details like if the dungeon is natural or worked stone, or what the natural light source is. I have to write those in advance if I'm going to say them at all.

And prep is not just about figuring out what you can improvise versus what needs to be planned. It's also about figuring out what's efficient in your game. If I put the time in I can make a really nice looking map. But the way I run games, having a map prop doesn't really mean that much. I was crushed when I spent 6 hours on a map and the players looked at it for all of 30 seconds. All the info they wanted was that there were mountains between them and their destination. I could have told them that. I could have made it up on the fly. It didn't take long for me to learn that map making was a time sink. I no longer do maps in prep because it doesn't give back enough game for the amount of time it takes to write them.


For me, prep takes three forms, and each has a different level of detail required, and so a different amount of work to be done:

Plot outlines, which I try to have a good deal planned out. Roughly I know what's likely to happen for the next year or so of gaming, assuming we stick with the campaign we're in, and the players don't throw any major curve-balls at me. Most of this is in my head, and if I were to take the time to write it down, it would probably be a few paragraphs long.

Places, which I try to have a list of interesting locations, names of a few people, and the occasional plot hook.

And encounters, which I try to have next session, maybe the following session, and a couple of semi appropriate one offs for when the players take me by surprise... "What... your heading into the woods to follow up on that other thing from ages ago, rather than trying to catch that pickpocket... good thing I've got this bandit camp/angry dryad/something". For encounters I put together the map and stat out the opposition as well as note their motivations etc. For one offs that go unused for a while, they can be periodically level'ed up so that they remain interesting to the players,


Depends on what you think your players will do, if your players will just do whatever you ask of them without really thinking outside the box. Well you shouldn't plan very far in advance. However if your players might throw a curve ball at you, for example tunneling through your maze of DOOM instead of actually going through it like people usually do. You might want to plan a bit further ahead. I wouldn't really worry to much about 'wasted content' anything that you didn't use can always be revamped, reworked, and reused later.


I'd also like to add that how much prep can even vary from game to game. 3 campaigns ago I ran a thieves guild game. When they weren't dealing with the main plot, the PCs were doing heists. But before they could commit to a heist they had to plan it.

They really got into the planning, often spending more time planning than heisting. After a couple months I realized the challenges they imagined for themselves were way more interesting than the ones I'd come up with while prepping. Or they'd attack from a vector I never could have foreseen and I'd have to improvise. No matter how much prep I did, better ideas emerged over the course of the in game planning session.

So I ended up doing this part of game prep during the game. I wrote down each hazard they thought they might encounter and deployed those once they got to the heisting. Sometimes I'd figure out a way to keep their plans from working. Other times I'd throw out hazards just to see their clever plans work out.

Anyway, the point is that in this one particular campaign I had to prep differently. It won't just vary with the GM or the players, but with the campaign as well.

  • \$\begingroup\$ When we were planning or talking things through in detail one of our GMs would sit and listen whilst holding up a sign saying "You're giving the GM ideas." and see how long it took us to notice. It quickly became a running joke that others, including myself, now use too. \$\endgroup\$ Commented Feb 4, 2011 at 12:45

Here's a very simple idea that changed a lot of things for me.

Every session, the players show up and they improvise what their characters will do without any problems. What if the GM could do the same?

My biggest prep is the first session. I come up with a situation, a bunch of NPCs. I give the NPCs motivations that will conflict with the PCs and/or each other. I maybe list some probable issues/logistical concerns that may come up as well. Then I just play the NPCs like I would a PC - they follow their motivations, they adapt and deal, sometimes making better or worse choices.

After that, each session, I just pay attention to what major things went down, how the NPCs are doing, and figure out their general attitudes or tacks on things. Obviously, if the game is very crunchy balanced about combat, that requires building a few encounters up to have on draw as needed, but I tend not to play that kind of game much anymore so it's easy to adapt and improvise.

My usual prep between games is 10-20 minutes of "Hmm, who is probably doing what, in general?"


How much prep? It depends on both your player group and GMing style.

If you have a good and readily accesible, organized collection of maps, as little as none.

There really can be no answer in hard hours... provided you don't feel unprepared during the game, you've done enough for you.

  • 1
    \$\begingroup\$ Second this. You need to prep as much as is necessary to accomplish your goals, which goes from none at all to a lifetime depending on what you seek to accomplish. \$\endgroup\$
    – Epiphanis
    Commented Dec 12, 2013 at 19:44

I find the most important thing I can prepare is knowing what would happen if the players did absolutely nothing about anything:

e.g. I recently ran a Cthulhu game where the players got trapped in a room of house between dimensions. If they players ignored the clues and just played cards they would run out of air and die. Hello, incentive!!!

I check for weak points in the plot or things I need players to do to advance the plot. I either change the plot so it does not have these weak points or just work out what might happen if they exploit these weaknesses and make it part of the game. I check for ways that a character could actually break the plot and prevent it:

e.g. my Cthulhu game (mentioned above) involved a specific dagger that was required for a ritual. One planted player knew what it was and might not want the ritual to do ahead and therefore would damage the dagger or a player might become insane and throw it out of the window etc. Hence the dagger's backstory contained information about how it was indestructable and the nothing could pass out of the room's windows or doors due to the spell used to get them there.

I knew the NPCs and what they were trying to achieve and combined with the background of the world events in my head I could adlib the rest.


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