You should take an official practice test (never a company test) before you start, so you know what the real GMAT is about, so you can get a rough idea of how much time you'll need to reach your goal, and to determine how to apportion your time between Quant and Verbal study.
You'll find lots of suggestions about study plans if you search this or other GMAT forums. As long as you work from high quality materials (you should mainly use official questions for practice, but should find a good unofficial source for explanations) there are lots of different study plans that can work. You should work systematically through each topic until you feel comfortable with each, and once you feel confident in your foundation, be sure also to work on test-taking skills (pacing strategy especially).
You might want to deviate from a decent but generic study plan, depending on your background, current level, and target score, so with a bit more information experts here might be able to give you some guidance specifically catered to you.