I used the Official Guide book and the computer GMATPreps. I took a sample test every two days for about two weeks before the exam. This averaged to 6 hours every week.
Honestly, I browsed through other books including Kaplan and Barron's and I think while practice is important, doing sample questions over and over is not the best strategy. Instead of doing multiple books, I constantly reviewed the questions on the OG that I got wrong, noting tricky mistakes and re-taking the computer GMATPreps and getting used to test-taking situations. Timing yourself is VERY important, pacing is critical, and so growing the stamina to tackle the exam is the most worthwhile way to increase your score.
Regarding math, I never tried to solve the DS question if I can avoid it. Unless it is some number crunching that you need to work out, I avoid it by plugging numbers and doing trial and error. It works out faster that way. Sentence correction is fairly straightforward, and used process of elimination and made sure I read every question. For critical reasoning, I always read the question first (but not the answers) and browsed through the essay several times, reading quickly first and meticulously scrutinizing the context for each specific questions.
I hope this advice helps - I was recently offered a chance to retake the examination (because the temperature of the room was 85+ degrees on my test day) but I did not choose to retake it. However, I am hoping they will note the unusual circumstances on the score report. Do they usually offer re-tests? I thought it was slightly bizarre, since they could not get rid of the old score anyway.
