How should I go about preparing for drama camp?

Practice a lot of vocal warm ups (for vocal projection and clarity) and work on those accents! Also, I recommend that you find a decent monologue that reflects your strengths. Some people are more comfortable doing comedic pieces, some more dramatic. A great thing to do is research the plays that will be performed, and find a piece that would put you ahead of others for certain roles. Oddly enough, about half the girls from previous camp experiences always pulled up a monologue regarding rape. It actually became so commonplace that I tried to find a piece from the raper's perspective, mix it up a little :P Anyway, best of luck.