What New GM's Should Avoid?
There are some easy rookie mistakes new GM's tend to make. These are not because they are bad GM's, simply that they don't know the best way to handle things since they lack experience.
An experienced driver knows how to drive fast, but when you get behind the wheel the first time a good instructor doesn't take you onto the autobahn with it's unlimited speed limit. Or onto a race track with other drivers on it all going 180 MPH.
Similarly new GM's should avoid certain things when first starting out. Eventually you will figure out when exceptions can be made, but avoiding them at the beginning will help you run things more smoothly.
This is supposed to be a place for new GM's to get tips from older more experienced GM's, and as such I think we should start here.
Here are a few things that I think new GM's should avoid:
1: NEVER play a character as the GM. The difference between a GM PC and an NPC, is leveling. If the character is sticking with a group of PC's and levels along with them, gets treasure, etc. That's a GM PC. NPC's should never divide XP, loot, or be a major directing force. NPC's are there to fulfill story points, plot devices, provide flavor to the story, and/or provide help on an as needed basis for the story. They should be helping the PC's but not holding their hands.
You may wonder why a GM PC is bad, it comes down to this. You already know what's going to happen, and how to defeat the monster, trap, puzzle, etc. Plus it is nearly impossible for a GM to not favor his personal PC. This will tend to alienate a large number of players. And lastly, separating IC knowledge from OOC knowledge is difficult for a lot of players, it's nearly impossible when you are the GM and a PC, because you know why something isn't working, but your PC doesn't.
Example: You're traveling through a dungeon. There is a wall with a small hole in it that is far too small for anyone to get through. On the other side you can see your magical gem that you are here to find and return so the curse on the land can be lifted. The hole is there so the PC's know this is the place they are supposed to be. They know it's here, they've seen it. But you don't want them bypassing the entire dungeon with a dimension door spell, or other quick magic. so you've placed a god level anti-teleport field on the dungeon. (The people responsible for the curse on the land are cultists to an evil entity, and this is unhallowed ground.) Your party's spell thief tries to Dimension Door to the gem and bypass the dungeon. But of course fails. The PC's get frustrated, they see some of the opposition and even a glimpse of what might be the boss fight, and don't understand why it's not working. They may ask your character why it's not working, now you have a dilemma you as a GM know what is going on, but your character? Does he know? If you simply always answer yes, you become the easy person to ask for all the answers when it gets difficult. If you say you don't know, the players will begin to see you as useless when figuring out the plot.
2. You shouldn't roll the dice for your players. This is a little less important during PBP games, since if someone can't get online during a critical scene and their turn is up you may have to do so. But in general it's best to let the players roll their own checks.
There are more to come, but this is the first post, and I'd like to get other GM's to post.