Sign up to take at least one AP course during your junior or senior years of high school. The availability of AP courses ranges widely from school to school, so if you're unsure of whether your school offers the class you want to take, ask your guidance counselor.
Get in touch with your school's AP coordinator about registering for the exams. If you're in an AP class then your teacher will probably already have taken care of this. If you're a home schooled student or are studying independently for the exams, ask the nearest school that offers the exams if you can register through their program.
Prepare for your exams by working hard in your classes and studying on your own. The amount of credit you receive for your exam scores relies on how high your scores are, so give it your best shot.
Choose which colleges you want to receive your scores and list them on your AP exam answer sheet. The scores are also sent to you and your high school, and you can have more copies sent out later if you need to.
Check to see what the crediting policy is for your particular college or university. You should be able to find this on the school's website. If you can't find it, then research it with the "AP Credit Policy Info" tool located on the College Board's AP homepage (see Resources below).