I'm not an expert when it comes to GMAT, but i'll tell you what has worked out for me so far:
1- Go over the material from OG11, quant and verbal guides too.
2- Record every type of the questions in quant in a different sheet or card and try to understand the concept behind it (for example: did u know that 2^3+2^3 = 2^4?).
3- After you are done with the first two steps, which will take you around 3 weeks, try and take the first
GMATprep and see how you do.
4- Record the questions you have answered wrong and try to find their correct solution from this forum, gladly the people over here have almost answered any questions you might think of, including the ones you've answered wrong/right in
GMATprep.
5- Obviously, if you have studied all types of questions from OG11 and the supp. quant and verbal enough, those questions you have answered wrong were not among the ones you have recorded in your sheets or cards, you add them to your sheet.
6- take the second
GMATprep and so on..
I hope this strategy helps,
good luck