Thought I'd chip in my 2 cents on verbal preparation:
1. It's going to be very hard to get a high score if you don't speak English as a first language (and even then, if you don't speak it well). I don't think there's any way around it. To compensate for this: READ everything you can as preparation for the GMAT. Read the NY Times, Wall Street Journal, google news, cnn... anything you can, so that the verbal section becomes a bit manageable. This isn't something you can prepare for in a month... it's going to take several months of reading regularly to improve your overall verbal (assuming you're a non-native speaker).
2. Sentence correction: Arguably the easiest part of verbal to improve in. The
Manhattan GMAT Sentence Correction book is a must buy, unless you're getting close to 100% right in your practice tests. It's not a terribly large book, and it's very easy to follow.
3. Reading comprehension: Arguably the hardest part to improve in, especially for non native speakers (see #1 above). I didn't use any specific book for reading comprehension. I did take several full length practice LSAT tests in the past, and those contained several reading comp passages. However, the LSAT tests don't give you an analysis of the right or wrong answers, so I wouldn't recommend them as a study guide.
4. Critical reasoning: I've been meaning to do a quick analysis on this because, based on what I've read, most 700+ posters on here have studied verbal using the LSAT Logical Reasoning Bible. The strategies they give are advanced, and many might be too advanced for the GMAT. However, I felt very prepared after studying this book, even though I studied it awhile back.
In my eyes, therefore, there are 2 clear "must buys" - the
MGMAT SC and the LSAT CR Bible. One final word of advice - don't buy loads of different books in hopes of learning more than 1 strategy. You're going to waste a lot of time and in the end it probably won't help your score. If you're going to buy another book for extra practice problems - then that's ok. But don't forget you'll also have access to plenty of practice problems if you buy the
MGMAT SC book (it comes with 6 free full length CAT tests and explanation of answers).
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