What I did was take the first 3 BC practice tests of each section at random, then the final two exams were done as a full length test. I would also recommend topscore, their sciences were pretty good (non sciences weren't that great). I also liked Qvault although a lot of people believe otherwise so I'd use that for more practice. Basically at the end of your studies you should be taking a lot of practice exams and review review REVIEW!
