I just finished taking pictures at a festival. It was loads of fun. Not much advice to be given-just don't be shy about going up to someone to take a picture. You'll miss a lot of great shots if you're shy.
Anything that looks cool, different and interesting, take a few different shots at different angles and views. Anyone dressed different too...stop them, tell them you're the "event photographer" (they get impressed with that title) and say, "wow, cool clothes, can i take a picture?". I've never been turned down.
Mingle around with everyone too. I got extra jobs by talking to people there. It's a great place to promote yourself.
Good luck! Don't forget to share you pictures here afterwards!