We just spoke a couple of days ago with a student who made a very solid score improvement and I think you might find this students' perspective helpful. The student had taken the January exam and got a 27 (~503), then took Altius and a September MCAT-2015 exam and got a 520. She said that by far the biggest difference was that the first time she focused very heavily on her prep book and science content. She did a ton of flash cards and committed a lot of vocabulary to memory. The problems she was doing were also mostly focused on mastering content. The second time around, she did almost exclusively exam review. She took all of the Altius full-length exams multiple times and spent 1-2 days PER EXAM reviewing and analyzing. The second time she was only focused on the exam itself and strategy in dealing with passage-based questions. She took 13 FLEs in the last 30 days.
She did not mention this on her own, but I also know that her time investment and the seriousness of her commitment were much greater the second time, as evidenced by things like dropping some extracurriculars, treating every single missed question like a big deal, etc.