I took the GRE last November. In August, I had taken a sample test on the internet, and had a total freak out moment when I realized I could not answer a single math question. Not like, I made a mistake and got the wrong answer, I had absolutely no idea what any of the questions meant. I was always pretty lousy at math in high school, but having not had any math classes in eleven years, I was now totally lost.
I bought this book and spent probably about three to five hours a day studying math. Doing word problems over and over again until I understood the concepts. I memorized geometry formulas on flashcards. (I was a teacher and it was summer, and then school was held up by a teachers’ strike that lasted a couple months, so I didn’t have much else to do.) I also had the Barron’s general prep book, which had several practice exams and I still did craptacularly on the math section every time I did it, so I was pretty nervous going into the test. I just had my fingers crossed that the computer adjustment factor would improve my score.
It did. I had been getting in the 450 range on my practice tests, and on the actual thing, I got a 600. I was elated. (That’s actually quite a bit better than I did on the SATs, and I had actually been taking math at the time.) All that studying paid off - without it, I would have certainly scored under 500.
Verbal is harder to study for, AFAICT. I subscribed to a bunch of word-a-day emails and went through the Barron’s book list of commonly used words, made lists of all the words I didn’t know, and made flashcards for all of them. I don’t think one single word I memorized was actually on the exam. I got a 720, but I can only assume that’s thanks to a lifetime of reading.
I had taken the GREs before and was surprised at how poorly I was scored on the Analytical section. This time around, I read the advice in my Barron’s book really carefully, and I did much better. The readers are looking for very specific things.
ETA: I agree with JustAnotherGeek that the math section on the GRE is about equal in difficulty to the SAT, but the verbal section is harder. I don’t know why that is. I did better on the verbal GRE than I did on the SAT, but I guess the extra years of reading helped, whereas I didn’t learn anything more about geometry in the intervening time.