Just to add to what's already been said, one key aspect is to regularly take practice CATs to assess how you're doing and see whether you're improving in the key areas. If you sign up with any of the major prep providers (Kaplan, Princeton Review, MGMAT, Knewton etc.) you will be provided access to 4-6 CATs. Each provider also has 1 free test you can take from their websites. So those tests together gives you at least 6-8 practice tests as resources. Combine that with the 2 GMAT Prep tests, and you can space out practice tests, doing 1 a week or so, over your entire study period. After each test, you can review results and chart errors, and work to improve your weaknesses before the next test.
I'm just starting out with studying for the GMAT though, so my comments might not be the greatest advice haha. I'm outlining my study plans and results as I go on my blog (
https://carlincognito.wordpress.com/) if you want to check it out!