Your first day of class

Here are some tips for your first day of class. NOTE: Schools vary, and some wont let you "roll" for several weeks when you start.

Come to class clean. But dont shower right before class unless you stink. The natural oils on your skin protect you.
Clip your toe nails! Clip them short, but not so short that its uncomfortable.
If you are allowed to roll, you will get destroyed beyond anything you could imagine. This is NORMAL. Dont think you suck at this, and quit. Jiu jitsu is simply that effective. It takes at least a full 6 months of training before you are really hanging with anyone ok.
Watch some youtube videos on how to properly tie your belt before class
Do NOT eat within 2 hours of class. You will very likely get sick. Its a hard workout, especially if you roll.
Bring a big bottle of water
Most classes begin with a warmup+stretching, then technique, then live sparring
Do not roll with anyone that has more than a 20lb weight advantage over you, if you have any choice in the matter