1. Be committed. When I DM I spend hours every week prepping for the game, and I expect the player to show up and be on time. This also includes leveling up your character on your time, not session time. The only thing I require is seeing the HP roll if you don't take the average.
2. Develop your characters. I am not here to spoon-feed you a story for you to react to. I play like real life: have goals, dreams, and things you want to accomplish. Otherwise, why would your character risk their life?
3. Be respectful. Everyone's voice should be heard and their ideas matter. When someone else is talking, let
them finish. If you continue to interrupt to steal the spotlight, this will become a problem.
4. Know the rules. I don't expect you to know everything, but you should know your race and class features, especially spells, without having to look them up all the time.
5. No drugs or alcohol. I don't do them and don't want them around. My friends don't do drugs either. If you smoke, you do it outside or in the garage, we don't allow smoking in the house.
6. Keep in-game problems in-game. I am fine with characters messing with other characters, stealing, killing even, if it is appropriate to your character and in character. If you are upset and do something like this just to get the other player, I won't allow it.
7. Keep out-of-game problems out-of-game. Same principle. If you have an issue with another player, leave it off the table. If you bring it to the table, you'll be asked to leave until the problem is resolved.
8. HAVE FUN! I run a serious game, but it is just as important to enjoy yourself at the table. We joke, and such, and sometimes it is a bit off-color or inappropriate, but we never mean offense. If you are at the table, try not to be too sensitive about it, it is all in good fun and we laugh at ourselves a lot.
As far as my style of DMing, I let new players know:
1. The dice rule. If you do something stupid, I'm not going to save you if the dice go against you. Even if you do something smart, I'm not going to save you. Risk is part of the game, and without it you might as well just go read a book.
2. I am traditional. I don't like crazy races as PCs unless you have a VERY good compelling story as to how and why you are trying to adventure with races who would normally see you as a threat.
3. #2 being said, not everything evil is evil. A party might encounter a tribe of hobgoblins, just trying to establish themselves and build a community. You don't have to kill everything you meet.
4. Bad stuff happens, but it is never graphic, only implied. Getting graphic about such things is never necessary. They happen, sure, and we all know it--so let's leave it at that.
5. Your characters can do whatever they want and are capable of doing, but expect the consequences--for good or bad.
That's about it.