Start learning Calculus the summer before you take the class. Start by developing a high-level view. You can use the attached document to have someone who understands calculus describe the view from 30,000 feet to you:
I found this summary of all AP Calculus (AB and BC) a few years ago on the internet. I wish I wrote down the developer of the document. Thank you!
AP Calculus Summary Quick Reference
You should aim to score a 4 or 5 on every AP test. With either score you should receive college credit at just about every college and university in America. To score a 4 or 5, you need to take lost of practice tests, score them, and review the results to see what you need to do differently to improve on the next practice test (and ultimately, the actual test).
Here are resources that are useful for preparing for the AP Calculus AB and BC tests:
AP Calculus Course Description (AB and BC, 2016 update)
AP Calculus Course Description (AB and BC, 2010 version, practice questions)
AP Calculus Multiple Choice Question Collection 1969-1998
This is a great resource. As this is no longer available from ETS for purchase, it is considered fair use to use for educational purposes, although I can't make it available as a download to all.
2008 AB Released Exam - Multiple Choice 2008 AB Multiple Choice Answer Key
2008 AP Calculus BC Released Exam - Multiple Choice 2008 BC Multiple Choice Solutions (Ask Mr. Calculus)
Related Rates: I found this summary document on the internet a few years ago. It's a great summary of the common question types. Once you understand the solution process, the key to solving each question is knowing the "setup". I believe it was created by a teacher in Utah: