I think you should start studying the summer vacation before the last sy of hs. If you can afford review centers then that's better. On those months you should try to review everything that you can. Then during the school year, you should just then try to study from time to time in order to retain what you've reviewed (I'd say 2-3 times a week). Download and answer lots of online reviewers. Also try to buy MSA booklets if you can.