You can find the previous AP Exam questions at ChemTeam . Of the two part of the exam, I have found the open response section to be the most important part. That is the part that would most likely determine your grade. Do the problems first and then the essays. Show all the work, and be precise.
Units are very important.
Make sure that all of your answers have proper units. Essays will be on the main concepts of the course. They are usually not very hard. Problems also are not very hard. You can expect at least one of the problems to be on the equilibrium.