Suggestions for studying / prepping for the GMAT

Question for the money board -

I am signed up to take the GMAT the last weekend of June. I bought the latest version of Kaplan and using that as my study guide. Without studying or cracking a book I took the pretest and got 48/78 questions right which accounts for a score estimate of 470-520 (granted this was a paper test and not the computer test which doesn't account for the difficulty algorithm or time, even though I tried to stick to 75 minutes per section).

Anybody here that has taken the GMAT have any advice for prepping? I have been trying to devote a couple of hours a day to studying (some more, some none at all depending on schedule). What worked for y'all? I am trying to get above a 630 overall score which would easily get me into any PMBA program here in Houston I want to go to.

By the way, the data sufficiency kicked my butt on the practice test I took. Also, quite few math problems seems to be just reviewing and remembering how to do basic 9th-11th grade math (is the math any more difficult than this?). The English part seemed pretty straightforward with a few tricky case studies.

Any help and recommendations would appreciated