Read over the syllabus for AP Biology if you have received one from the teacher. This will serve as a guideline, letting you know what to study during the summer.
Prepare by getting a copy of the textbook you'll be using to study from during the summer. If the AP Biology teacher has not given guidelines for summer prep, use the textbook as a tool for becoming familiar with some of the concepts you'll cover. If your school won't lend you a copy to keep for the summer, try the local library.
Buy a review guide for AP Biology or for the textbook you're using. It should like a small booklet or pamphlet, and it should have outlines for major topics in AP Biology.
Make flashcards for the vocabulary terms that you'll need to know during the course. You can study the flashcards all summer long and have a friend or relative quiz you. Flashcards may not give you an in-depth exploration of the things you'll be learning in AP Biology, but at least you'll be briefed on the terminology come class time.