1. Be fair - If you are arbitrary in your rulings or make judgment calls against the players just because you don't like the way things are going even though everyone is playing by the rules it can sour the game for everyone. The first thing to remember is these people are your friends most of the time and even though there is an adversarial relationship don't lord your role of power over the players and make them resent your role. Players that are unhappy start missing games or quit entirely and that's no fun for anyone.
2. Be firm - When you do make a call most of the time stick to it unless it was an honest mistake then you can take it back if you want. Realize that your word int he game is the final one that's the main purpose of the role, to arbitrate and create the game. If you let players run ruff-shod over you by rules lawyering or whatever it reduced the fun of everyone involved, often including the player doing the harm. They may get temporary enjoyment out of sneaking by you or arguing that they are right till you give up but in the long run its less enjoyable even to them. On thing I always say when a big argument about something happens is lets talk about it after the game but lets go with my call for now and we can discuss it later. Most players this is acceptable and it helps keep tthe game from getting bogged down in fights.
3. Be fun - If you arent having fun running the game chances are your players arent either.
4. Be consistent - If you rule that zombies are immune to holy water when it benefits you, its only fair if its true when it benefits the player as well
5. If your not sure you can always be at the game, don't game master let someone else do it. Nothing is worse then having everyone show up and realizing there's no game cause Jim had to work the 3rd shift or whatever.
6. Don't be afraid to pull things from pop culture, Books, movies, music, and video games are ripe with ideas for your games. The trick is not to do it verbatim but take the spirit of the idea and make it your own. I often draw on sources of books I've read. If you have ever read Simon R Green's Deathstalker books I used a section where a planet was populated by toys in one of my D&D games. I didn't use it exactly like the book and the outcome was much different, but I used the bones of the story to create my own fiction. Its one of the more memorable games I've run in recent years as well.
7. If a player wants to do something odd, don't say no out of hand, think about it and if its possible say maybe and let the dice decide. I have a couple of players that often try to gain advantage by doing weird things. For instance If I put a set of stairs with a banister in a room with the bad guys at the bottom, my friend Aaron will almost always try to slide down that banister with sword drawn all Errol Flynn like. I don't tell him he cant I just make him roll dice to see if he makes it or fails in some amusing way.
8. Don't get bogged down by combat. Often new GMs get really into throwing monsters all the time, and that kind of game can be fun. However remember that the best games are ones where it feels like you are participating in a real story. Where your actions have consequences. Some games all the players ever do is raid Dungeon XYZ, Plunder it then return to town for some well deserved whoring and drinking. But after 13 years of running D&D I don't remember any of those games at all, its like the difference between a snack and a meal. Dungeon crashing is a candy bar, A well developed story arc is a Steak.