Collect your Calculus notes, your textbook and homework to review the material from the entire year. It's often best to work chapter by chapter. Revisit the important terms and concepts, explore different equations and revisit the homework problems from each section. By reacquainting yourself with the material, you will refresh your memory and give yourself some much-needed practice.
Utilize an AP study guide or other online assistance to help with your studying. Bookstores carry an assortment of AP study guides, which feature helpful hints and thousands of practice problems. Getting used to the types of multiple choice problems you will encounter on the actual AP exam is especially useful, as they are probably somewhat different from what you've grown accustomed to in class.
After reviewing your material from class and studying with an AP Calculus guide, be honest about your strengths and weaknesses. Once you've diagnosed your weak area, zero in on it. There is no need to waste time by studying the areas you have already mastered. Instead, focus your attention on practicing problems with which you remain uncomfortable.
Form a study group with some of your classmates. Sometimes, reviewing challenging problems or going over difficult concepts can be more effective with the input of a group of people. In study group meetings, you can also quiz one another to practice answering calculus questions.
Don't be afraid to ask your teacher for help. If there are concepts you still don't understand or a problem you are unable to solve, ask your teacher for a time to meet up. Often, teachers are happy to set aside a little time to help their students. With a little extra attention and additional explanation, you may find some challenging topics of calculus significantly less difficult.