I'm sorry you didn't get the score you wanted the first time around.
Combo is right! How long ago was your last practice test? If within the past 2-3 weeks, that's fine. If not, take another now. Go through the test and pick out the specific areas on which your percentages are too low (<50%), your time is too high (>2.5m), or both. Use your specific weaknesses to drive your review.
For each question, figure out:
- specifically why you got it wrong, or why you went over on time, or both (note: there may be multiple reasons)
- what you need to do to minimize the chances of making that error again.
[did you not know the content? return to the relevant chapter in your strategy guide. did you not know the technique? ditto. did you know the content and technique but mess up on the execution, often known as a "careless mistake?" how are you going to do things differently next time to minimize the chances of repeating that type of careless mistake? did you know the content and technique but just took way too long to do it? figure out the most efficient way to do it going forward and figure out how you're going to recognize that shortcut (or those shortcuts) in future. did you not know either the content or technique and spent way too long? learn how to recognize before 2 min are up that this problem is not going to happen for you. then learn how to make an educated guess (eliminating some wrong answers before guessing). Then guess at or before the 2 min mark. Those are just some ideas to get you started. :)]
- all of the better ways you can think of to do the problem (in math, there are always multiple ways to do it; "better" ways are the ways that are specifically better for you)
- how you will recognize a problem of a similar type in future so that you can apply all of the above to that new problem; essentially, recognize what to do, do it, and move on (note: "recognize what to do" also includes "I should make an educated guess on this one")
Okay, now, you do the above first with questions from your practice test. Then you use that to drive which chapters / concepts you need to review from the strategy guide. Then you do a *few* OG questions to test yourself (and time yourself and do the same kind of analysis on those OG questions). Then you also do mixed sets of problems, chosen randomly, and as you uncover more weaknesses with these, you repeat the cycle with the strategy guides.
You might decide, for example, to do a set of 15 problems, 7 DS and 8 PS. You pick some random problems out of OG numbered between 50 and 150 (or lower or higher - depends on your ability level), but spread out over a range of about 100 questions, to have some easier and some harder ones. Mark the pages so you can flip to them easily, set the timer, and go.
You may also want to look into GMAT Focus (
www.gmatfocus.com). This is a quant-only diagnostic test made by the real test-writers. Not free but not too expensive. It will give you problems that aren't in the OG (but are still real GMAT problems), time you, and give you analysis on your strengths and weaknesses as well. (Note: last I checked, GMAT Focus didn't hold you to a time limit, but it did time you. If it still doesn't give you a limit, still try to hold yourself to that 2min per question average!)
Good luck - let us know how it goes.