One of the first adventures I played (as GM) was E1 (Der Alchemyst). It is part of a campaign, but can be played stand alone without limitations. But I'm not sure if it is available in English.
I don't know the English names of skills and other system specific parts. So I will try to translate them and mention the German word in parentheses.
Introduction to role playing
If this is not only a system introduction, but also an introduction to roleplaying, you first need the player to get a feeling that there are no restrictions in what they can do (consequence yes, restrictions no) and that they do not just play your story, but forge it with their actions.
In my opinion this is an important part of roleplaying: use common sense instead of rules to keep things smooth and simple. There are rules for almost anything (literally), but you risk to overwhelm your players at this point.
In this stage you also need to act as a moderator so any player is participating. If you have dominant players they can easily take control over the complete group. Try to encourage shy players with 'random' events/interactions to let them choose there own actions.
Introduction to the Talent System
After your players getting feel for their character, they need to know what he is capable of. Let one of your players roll a skill check and give him a bonus on this test (he should pass the test). You can then describe how a skill check works and how boni and mali apply. Shortly after this you should let the whole group make a skill check, so that every one can roll dice and calculate how many skill points remain. For the latter one I would suggest perception (dt. Sinnenschärfe).
Introduction to Fight
Instead of a battle with the complete group I would start with a short fight with only one of your players. Something like a contest. Maybe a wandering swordsman wants to let his pupil train with him. Because it is a one-on-one fight it will be easy to gasp for every one. Also making it a non life-or-death situation helps your player focus on the 'how to fight'. Also the fight will be ended after a short amount of rounds without wounds (only some live points will be lost). Using a human instead an animal also lets you introduce special maneuvers like feint (dt. Finte) that the opponent can use to make the fight a little more interesting.
Introduction to Magic
You should skip this when you have no mage/witch/...
It is most likely that a mage player will want to use his magic early in the game. However if your magic user is something like a witch call him to attention that he does not want anybody to know that he actually uses magic. Not even his group (which he maybe met a couple of days ago).
Introduction to the World
This is the trickiest part. You can give your players a short introduction of the world and the gods before the play and that is (depending where you actually play) orientated on a specific time period.
You should not pack everything in the first adventure. Pick only one or two aspects in detail.
- Let a votary (dt. Geweihter) of one of the main gods appear and interact with the group or let them perform miracles. (In later sessions you can start introducing lesser gods like Aves.)
- An easy part is the gender equality. Let women appear in jobs that where men dominated in our history. Like Guards, Woodcutter and official politicians.
- For your adventure of course also law aspects.
- I wouldn't use many fights. Those cost much time. Maximum one big fight and a medium or two small. What a small fight is depends a little bit on your group. You can start with a knight or rondra warrior that is capable to hold his stand against two guards without problem. An ambush with some thugs would for him be a small fly, while for group which best fighting character is a dwarf smith this could get already challenging.
- I wouldn't be sure about using poison on a character. You could put him out of the game until he is cured. Even if he can still move giving a start character some mali will render him almost useless whenever he tries to accomplish something over skills.
- If you want to use the poison you can poison an NPC that the group depends on. Maybe he got some information or can transport them over a river.
- Regeneration and healing can already be introduced through the fights. It is unlikely that your group gets through it without a screech. You can postpone poison and illness for later sessions.
- Don't use 10+d6 days to solve the puzzle or die mechanic. Why +d6? This sounds like some generic quest generator. There is a reason it takes 11 days or 16. And as a GM you should have control and not the dices about how the world works. The time your group has is an elemental part of the plot and how you plan the events on their journey.
- You maybe should not kill the group at the end. When I get it correct you want to show them that the World has consequences and that their characters can die. However this experience can be demotivation for players. You should first encourage your players before showing them how cruel the world is. This will motivate them for the next sessions.
- Show them that characters can die when they get to over confident. Your overall goal should be to have fun. Demotivating the group is not the best method to let them remember the session as funny as it was.
- Especially in the first adventure the group should succeed somehow as long as they don't behave like idiots. If they fail it could be something like the antagonist got away but they still could secure the stolen material. It should be challenging but not to hard. It is not about if they play the character again but the moral of the group.
One last advice especially for investigative adventures: I often have seen GM's having a complete picture of the story in their mind and what should happen when. (I can't always exclude myself here (=_ =;)) But keep in mind that you should be open to suggestions of your players.
If they have an idea describe what's happens and don't just say it does not work or it will have no effect. After all, it is all about fun. The first time is not that bad when you say it, the second it gets unpleasant for the players and after the third time they will just sit there and wait what will happen next.
You have the plan they don't. If your group needs 3 clues to get the information they need, you need at least 30 opportunity's where they can get them. Half of the locations they won't visit. Another half of the time they will be interested in some other aspect of the current location. And the third half they won't get the clue because they fail some important skill check. This leads to 3.75 clues they gather (\$30 / 2 / 2 / 2 = 3.75\$).
In short: plan for many ways to solve this adventure not only one (and also for ways you haven't imaged). Let your group (and yourself) have a nice evening.