Chemblog!

Before (or during) your AP break assignment, you should consult your "5 Steps to a 5" Review book: at the end of each unit is a section called "common errors to avoid". For example, the most conspicuous error listed (which was a common error on our exams) is the (lack of) use of the BALANCED stoichiometric equation in solving a given problem (especially in thermo).
The lists of errors, which were compiled by experienced AP exam readers, is the most valuable part of that review book. Be wary of these errors as you do the problems.