I already took the LSAT and the GRE, so I know most of the topics covered on the GMAT I'm currently just using online CATs provided by my Kaplan GMAT classes. I am making progress by doing CATs continuously and going over my mistakes but I wonder am I doing this right or is there a better way to study?
The best way to study is the way that works best for you! It sounds like you've gotten quite familiar with the content for the GMAT almost inadvertently, so I'd say you should make sure to spend time learning these two things:
1) The format of the test and the particular kind of stamina that you'll need to sit for 4 hours with 4 different sections.
2) Learning how to pace yourself. The exam requires you to complete a different number of questions per section/hour than the GRE and LSAT.
Otherwise, use the CAT exams to measure your progress. As long as you're reflecting on your mistakes and figuring out where to improve next, you are on the right track for now.
