Take practice tests. Also, on at least 1–2 of the practice tests, do the writing section. Don’t worry to much about the score on the writing section (it isn’t figured in to your overall score), but writing for 1 hour and then jumping in to answer GMAT questions requires a bit of training.
Once you take a practice tests, look at the results. This will tell you what sections within Math you are weaker in. Spend time doing tons of problems on areas you are weaker in (e.g. problem solving, fractions, etc). Also, I highly recommend the Manhattan GMAT practice course. They provide great materials, the courses are taught by high quality instructors, and they give you 6 practice adaptive tests to take online. Remember, you won’t get better at the math section by avoiding it. Take a practice test, figure out where you are weak, and focus your time on improving in those areas. Good luck.