Here is what I would suggest:
a) Read National dailies, academic articles (less technical ones)--summarize in about a sentence or two what each paragraph is saying and what the full article is saying. Note down difficult words and find their meaning in context. Diversify your reading interests: for example, don't just read what's on the headline in the NYT but also read what's on the "Dine and Wine" or "Real Estate" sections. You will be amazed how much that will prepare you for the comprehension section in the GRE. Make it a habit, and it will not just help you for your test but will keep you abreast of what is happening around.

b) Of course, you gotta have a strong vocabulary. The only way to get better at it is by memorizing words and coming across in your readings. Memorizing only doesn't help. That's why a) is even more important in knowing the contextual meaning of words. a) and b) should go side by side.

c) Watch South Park