Hi, Isis

First, you need to get a handle on your individual strengths and weaknesses so you know how to spend your study time. Second, you need to incorporate analysis into your study, not just reading and doing problems.

If your last test score was a 500, then it is likely there are still content areas (math concepts / formulas and grammar rules) that you sitll need to review. As you learn the fundamentals for the different content areas, you then need to practice GMAT questions that cover each area. So, for example, first you might study triangles and learn everything you need to know about triangles. Then, you do some geometry questions (both DS and PS) that specifically relate to triangles. (Ideally, take these from OG - even if you've done them already, you still have a lot you can learn from them.)

After you do a problem, go back and analyze. Did I do it correctly? If so, how long did it take me? Is that acceptable? Is there a more efficient way to do it? How might I have gotten tricked or pulled away from the right answer? What are the most common mistakes people would be likely to make on this problem? How do I avoid making those mistakes in future? (Even though you didn't make them this time, you might just have gotten lucky - you should be as conscious of the mistakes you don't make as you are of the right steps to take.)

If I got it wrong, why did I get it wrong? How do I do it correctly? (Note that those last two questions are different questions.) How will I remember how to do it correctly?

Regardless of whether I got it right or wrong, what is it about this problem that tells me what concept it is testing? How will I recognize a similar problem in the future (that is, a problem that is testing the same concept, even though it is a different problem)? What will I do the next time I see a problem of this type?

You can spend 10 minutes examining one problem if you ask yourself all of these questions. When you get good at this analysis, you will probably only spend 2-4 minutes analyzing each question.