I went to a mediocre undergrad school and then got into my top choice for grad schools in sociology. Here are my experiences:
1. The verbal section is like the SATs, only with more esoteric vocabulary. Trying to fill your head with new words won't really work, as any number of words could appear on the test. You have to learn how to guess effectively.
2. The math section is EASY, covering only stuff up to basic algebra and geometry. Consequently, the percentiles are way skewed: a perfect score is only 90th percentile. The only way the questions are difficult is if they are trickily worded.
3. The writing section is new, but I found it to be the easiest. Honest to god, post-whoring on message boards prepared me for it.
Fuck the expensive prep courses. You can likely get a Kaplan book from your campus library (or something equivalent) and do some practice tests. I only studied for 10 hours, which was likely a mistake. I coulda done better.
The computerized test is weird. It has an algorithm that ratchets up the difficulty of your questions (and its predicted score for you) if you get a question right. Because of how it works, the questions at the beginning count for a lot more than those at the end. I don't know much about the paper and pencil test.
My particular admissions committee cared a lot more about my letters of rec and statement of purpose than the GRE. YMMV.
ebola