When I was studying for AP Chem, I did lots and lots of previous free response questions. They have the ones from past exams on College Board along with answer keys. Doing that was incredibly helpful because in my opinion, the free response was the hardest part of the test. I think there are also a couple of old multiple choice sections on the Internet as well if you look for them. If you have a review book, do the questions in there, too. Good luck!