Know what you want to get out of the program before you go down there, and set goals to make it happen. If you're going down mostly because you want a career in ______ and you know Disney has a great reputation in _______, that's great -- but know that, be able to articulate it, and be able to formulate a tentative plan that'll help you take advantage of it -- everything from classes to mentors to anything else. Things will change, but if you know what you want from the beginning, you'll have a much greater likelihood of getting what you want out of the program.
Take advantage of the things offered to you as a CP. There are special "Conversations with..." and "Career Insights" programs just for CPs, classes, behind-the-scenes tours, character breakfasts, social programming and all kinds of other things ONLY for CP's. Don't only go to things that your friends or roommates are going to. Take advantage of as many of them as you can - even if it's something you're only marginally interested in, because you never know what could happen.
Remember that there are three parts to the program -- living, learning, and earning. There is no guarantee that all of those parts will be perfect all of the time, but that's the great thing -- they all work together, and no one thing will entirely consume your life. Maybe your roommates suck, but you could absolutely love your job and your other friends. Maybe you're not thrilled with your work location, but you still get to go home to great people and take classes you enjoy. Balance is important, and hard to achieve at the beginning (you will feel like you are ALWAYS at work), but it's worth working hard to acheive it -- you'll be a lot happier.
For a lot of people, there is an inevitable slump after your first couple of weeks on the program. The excitement of actually being there has worn off, your roommates who you loved at first can't seem to do the dishes to save their lives, and haven't realized that taking out the trash means it actually has to leave the apartment, you're always at work, the amount of work you're doing doesn't seem proportional to the checks you've been getting, and you're just not sure if this is the right thing for you. THIS WILL PASS. Just do your best to get through it -- this is where that work/life balance becomes very, very important.
Bring your camera everywhere, and (though now that everyone has digital cameras, it's probably not so much of an issue) actually take and develop your pictures. Trust me when I say you will regret it if you don't -- there are so many times I didn't take a camera because we were just running over to someone's apartment, and we wound up doing something crazy I wish I had pictures of. (Like setting up a slip and slide in the very back of Chatham...)
Go places and do things outside of property and other theme parks. There is more to Orlando than Disney, Universal and I-Drive. There are restaurants that are not chains. There are more bars than the ones on PI, Bennigans, Cheers, and Jungle Jim's. Get to know the city you're living in, even if you're only there for 5 months. Being able to literally get away from it all is a great way to relax and let go. Check out the popular places up by UCF. Go to the art museum downtown. See one of the free popcorn flicks in the park presented by the Enzian in Winter Park -- bring a blanket, bug spray and a picnic. Go to a Magic game.
Most of all, don't be afraid to try new things. And have fun!