RIDE THE COURSE BEFORE THE RACE!!!!!
I cannot stress this enough. I broke my collarbone during my first race, which was an accident I feel I could have avoided had I known the course better. Do it at least once at a warm-up pace to get it mapped out in your head, and then again a little faster so you can start to figure out where you should and should not attack, where you may get thrown off course if you're going to fast, and where the barricades and run-ups are.
Also, if you've got a grassy area by your house/apartment, take a 20 or 30 minutes a few nights a week before your first race to practice your mounts and dismounts. Get the whole sliding your inner thigh onto the saddle thing down at your own pace. If you just go into the race without practicing your remounts, then you may accidentally mash your junk. No fun.
For your first race, the main goal should be to have fun, and ride safe. Worry more about getting to the finish in one piece, and less about place you're in. Remember, you're going to want to race again, so make sure you finish in a physical state that allows you to do so.