For some typical math geeks, for some non-native English speakers, and for assorted others, the challenges of the GMAT Verbal section can seem like a nightmare. Suppose you are so daunted by these challenges that you would be willing to exert any effort, take any risk, even sacrifice a virgin to any god who would deign to help you. Even if it were your life-goal to excel on the GMAT Verbal section what concrete steps would you take? Well, first of all, be advised that, outside of some of the boroughs of New York City, most municipalities frown on outright human sacrifice, and more importantly, the demonstrable effects of such sacrifices on GMAT performance are, admittedly, unclear at best.
In practical terms, one might think a profitable course of action would be to practice every single GMAT Verbal practice question on which one could lay one's hands. Practice most certainly is helpful, but an admonition is in order here. Focus on quality, not quantity. You see, most GMAT practice math questions, even if they are not excellent, are at least acceptable. It's relatively hard to write a truly atrocious GMAT math question. By contrast, it's astonishingly easy to write a truly abysmal GMAT verbal question, and not surprisingly, the web is simply littered with GMAT practice verbal questions of truly abominable quality. Caveat emptor. It is well worth your while to check out the very best GMAT books, because if you don't check the quality of the source first, you may well spend your time banging your head against some idiocy that won't help you at all!
Some folks think that they need to make a huge push in studying vocabulary, but that's not really the case. The GRE, the test for poets and literary critics --- that's the test that employs extraordinarily recondite vocabulary. For the GMAT, you do need to know basic Economics 101 vocab --- profit, cost, resources, interest, etc. --- but beyond that, you do not need to make a particular push to master vocabulary.
If the GRE Verbal is a test of words, the GMAT Verbal is a test of sentences. How are you going to get a large number of complex, well-crafted sentences to pass before your eyes? I have a magic one-word piece of advice: read. Read every single day, over and above any of your GMAT practice. Read academic books and articles, especially ones well outside of your field of expertise. Articles in the NY Times and Atlantic Monthly are also great. I highly recommend both the Wall Street Journal and the Economist magazine --- and, by the way, if an MBA is in your plans, it's utterly beyond me why you already wouldn't be reading these two crucial publications every day!
For what are you reading? Think of this reading as a three-fold task. First of all, of course, you just want to understand what is being said, what the text is trying to communicate. Practice extracting the "main idea", the "main point" of anything you read. Someone had to spend a great deal of time putting those words together, and if the writing appears in any of those publications, it means someone else paid them a healthy chunk of change for those words. What's the big deal? Why is this in print in the first place?
Your second focus while reading, not wholly distinct from the first: play attention to arguments. Opinion pieces are particularly good for this, and sometimes even advertisements can be used for this. Is there anything controversial, or debatable, of which the author is trying to convince you? If so, how does the author make that argument? What evidence is cited? What assumptions are made? What can you infer? What additional information would allow you to evaluate the validity of the argument? Keep your eyes open for any time someone makes an argument to you in any context, and be ready to bring this full set of analytical skills to bear.
Finally, when you read, pay attention to grammar. What are the nouns and verbs? What phrases and clause are used? What modifiers are used, and what do they modify? Can you identify the antecedent of every pronoun? Is everything said as directly, unambiguously, and effectively as it could? (In most of the above publications, the answer almost invariably would be "yes"!) A good GMAT source will acquaint you with the guidelines of GMAT grammar --- as you learn and practice those grammatical forms in your GMAT practice, also keep your eyes open for where these forms appear among everything you are reading.
As the astute reader probably realized, these "three modes" of reading are designed, quite specifically, to prepare you the three types of GMAT Verbal questions. Read every day with these foci, learn about the complexity of the world, and almost inadvertently, you will be well on your way to GMAT mastery.