I've taken the GMAT recently. And I've received a pretty good score of 710 (48/38 ) at the first try. I wasn't preparing very hard, just practicing simulated tests on the computer about 2 times a week for two months and 7 days of tough everyday preparation a week before the test. My English isn't ideal, though as you can see I received quite a good verbal score. In my opinion, GMAT defeating is quite a matter of strategies and luck. I would not reccomend Princeton Review book because I didn't find anything of value here. Moreover, I'm also not of a good opinion about other preparations tools like Kaplan, actually I met only about 25% of tasks in Math part of GMAT which are described in those books. In verbal section I advice the following:
in CR adhere to the passages as close as possible, don't infere to much, sometimes from our Slovenic point of view some answers would seem even too simple just a restatement of the said above.
in RC if it is possible try to eliminate wrong answers looking for references in the text every time, don't rely on your memory or understanding of the text
actually I didn't find SC part to be very difficult in GMAT, knowing "general" types of GMAT mistakes in SC it is just a matter of eliminating wrong choices.
Good luck.