1. **Focus Fire:** Don't spread out damage any more than you have to. It's far more effective for most of the monsters to concentrate on a single target. If you can get a player down, that's that much less damage per round Team Monster is taking, and the party is suddenly on the defensive to try to save the downed player (only particularly nasty monsters should take the opportunity to coup de grace an unconscious player). Which player should you target first? That leads to the next question...

 2. **Target the Squishies:** Monsters should always focus fire the available target with the least current HP & lowest defenses. That's who they're most likely to successfully take down. Brutes in particular benefit from attacking low-defense targets, since they have high damage but low attack. Note that I said *available* target, though. If a sticky defender is guarding a doorway, don't try to rush past him to get at the wizard. But if several monsters can get at the wizard...

 3. **Weigh Cost/Benefit for Marks:** If a monster is marked, you shouldn't have it automatically attack the fighter *or* always ignore the mark; only ignore the mark when it's worth it to do so. How much damage as a percentage of the max HP are you likely to do to the defender, versus how much are you likely to do to whoever else you could be hitting? If you're probably going to more effective against someone else, how much HP do you have left and how unpleasant is the defender's mark punishment? Remember that any target that has defenses that are lower than the defender's by more than 2 is easier to hit than the defender even when the monster is marked.

 4. **Control, Control, Control:** Make good use of controllers and leaders. Unlike damage, control should be targeted at the characters it will be most debilitating on. Immobilize/slow are for melee attackers, blindness & daze should be dropped on the biggest threats, and so on. Control has a *huge* effect on the difficulty of a fight.

 5. **Protect Your Squishies:** Artillery and ranged controllers, and when possible leaders, should be stationed towards the back. Use soldiers and minion packs to tie down melee players so that they can't get to your ranged units and to keep defenders busy so lurkers, skirmishers, and brutes can slip past to the party's weaker ranged units.

 6. **Use the Terrain:** Have your ranged attackers hide behind pillars (remember, if you're directly behind a one-square pillar, you have cover but enemy targets don't). Remember that monsters can use *each other* as cover if necessary. Position your frontline and backline to maximize the amount of difficult or dangerous terrain melee players have to go through to get past the frontline to the backline.

 7. **Alpha Strike:** Winning initiative helps; if your group simplifies initiative by having all the players go in order then all of Team Monsters go, or vice versa depending on which team won initiative, then winning initiative *really* helps. Monsters should use any encounter or recharge powers they have early & often. It's better to use it at the start of the fight in a slightly less-than-ideal targeting scenario than to save it for later and up dying without using it.

 8. **Encounter Building:** Picking the right monsters to use can make a huge difference in an encounter's difficulty, even when your options all have the same total XP budget. Here are some things to remember:

  1. *Frontline & Backline:* Try to have a mix of frontline monsters that are designed to keep melee players busy and backline monsters that are designed to hit hard. You will especially need a good frontline if most of your "backline" monsters have to stay in melee range (brutes, some skirmishers and lurkers).

  2. *Monster Synergy:* Pick monsters whose abilities complement each other. If you have a skirmisher/lurker that does bonus damage to slowed foes, find a controller with a nice AoE or save-ends slowing attack. Daze & prone is another nice combo, especially against melee players; immobilize & forced movement is also strong against melee players. If you have several monsters that give a bonus to adjacent allies, go heavy on melee monsters so more of them can benefit.

  3. *Terrain Synergy:* Are there a lot of hazards players will have to avoid? Bring lots of forced movement to try to shove them into it. Lots of terrain sources of elemental damage? Pick monsters that resist or are immune to that damage, so they can move through it with impunity. Lots of difficult terrain or features that block movement but not line of sight? Go heavy on ranged monsters so you can pincushion the players as they move engage.

  4. *Control Is Good:* Control effects, used properly, will generally be more effective than damage *if* you have a couple high-damage monsters to take advantage of them *and* you have some blockers to keep your control monsters from dying the instant the players notice them. Generally speaking, a good ratio is 30% blockers, 20% damage, 50% control. Remember that lots of non-controller monsters offer decent control effects, however, especially as you start getting into paragon tier (by epic, almost every non-minion has some sort of control).

  5. *Don't Use Pre-MM3 Solos:* This one is admittedly a little 4e-specific, but it's good advice nonetheless. Before MM3 solos depended entirely on having lots of HP to survive, but this meant a typical solo fight entailed the party stun-locking the solo for a round or two while the strikers went nova on him, typically ending the fight with little or no damage inflicted on the party. I've actually seen a mid-heroic solo killed in the first round by a single player (admittedly he critted with a daily power, action pointed, and then critted with a second daily power, but still). MM3 and later solos tend to have more ways to negate or ignore status effects (especially stun/daze) and more ways to interrupt multi-attack chains, thus giving them considerably more survivability.

  6. *Use Higher Level Monsters When Possible:* All else being equal, 4 level+1 foes will generally be a harder fight than 5 level-1 foes. Monster and terrain synergy definitely trump this one, though.

That said, not every monster is a tactical genius. Animals in particular will tend to just concentrate on whoever is closest or doing the most damage to them, and will almost always ignore defender marks. Dumber and more cowardly enemies (goblins, kobolds) will usually attack in a big pack, and will almost always respect defender marks.