Remember to enjoy the experience. I will be one of the most rewarding you will have. You will learn more that you think. Your supervisor is the best resource you have. There's no substitute for a good attitude.
Tough situations are an excellent time for learning.
Be safe and know there are other people you can count on for support. Get to know your residents - this will not only help out in community buildling, but will help you assess problems that might arise. Ask yourself how you would deal with ethical dilemmas - think about how you would deal with those questionable circumstances before they arise. Talk about these things before hand. Know your biases up front - think about the types of people and situations you have biases toward and realize you may have to deal with them in your position.