I aced the GMAT recently and have been fielding questions about how I did it so I thought I'd write it up for those who are about to embark on this adventure.

I hadn't taken any Math at all since high school so I was obviously concerned about the quantitative portion.  I started about three months before the test by going through a book called Forgotten Algebra.  It was a great refresher and worked well to give me a baseline.  It helped that I loved Math as a student and a lot of it came back to me pretty quickly.

The first thing I noticed is that while I was grasping the large concepts, I was making very small errors like thinking 3x2 is 5.  I tried to go more slowly which really helped with my accuracy.

The next thing I did was take a preparation class through Seattle University which I do not recommend.  I recommend taking a class, but there were so many problems with this particular class that I don't even want to waste my time and yours detailing them.  I'd go for a Kaplan or Princeton Review class.

After our teacher let us out early from our prep class one night (hello! that was $100!) I parked my butt at a Barnes & Noble and spent at least 30 minutes with every single GMAT book they had.  The Kaplan 800 is the only one I bought.

I then went through a general GMAT prep book (the official one - it's pretty basic) and wrote down concepts and rules on flash cards.  This was extremely valuable - I ended up using about 200 cards.  I included not only rules like The Laws of Exponents, but also quick ways to work common problems like work (johnny can do the job in 5 days and sally in 3 days and mark in 2 days, how long does it take...) or tank problems (it takes 8 minutes to fill a tank with pipe A and 3 minutes to empty a tank with pipe B...). 

Then I went through every single page of the Kaplan 800 book.  I found it quite difficult but it made the GMAT seem easy so I think it prepared me well. It is not a book that will teach you the quantitative stuff you have forgotten - I recommend a basic GMAT book for that - but once you've mastered the concepts, this book will really put your knowledge to the test. If you can go through the whole thing you will really be prepared for just about anything they throw at you.

The Kaplan 800 also helped me with the verbal sections by teaching me about specific errors they often present in the sentence completion section.  Reading comprehension is pretty easy and the analysis of an argument section is simple once you go through practice questions.  Most of the verbal section is logic and I don't think you can really prepare for it.

So I went through prep books for about 3-4 hours a night for the last few weeks leading up to the test. I found that more than 4 hours ended up making me a little mad and stir crazy ("Who cares if your mixture has 1/3 cashews and 2/7 peanuts!") so I tried to just be consistent about it and study every night. 

I also studied my flash cards periodically throughout the day until about 10 minutes before I sat down at the test and I'm so glad I did - the first question used the slope equation in coordinate geometry and I'm not sure I would have been able to figure it out if I hadn't had it in my short term memory.

Most people say the test is adaptive - that is the questions get harder if you get them right - and that you should take the time to do well on the first questions or else you'll be stuck with easy questions and a low score.  In my experience I think this is true, as I spent over five minutes instead of the suggested two on the first question and I'm pretty sure I got it right so the questions got increasingly hard.  Eventually they got too hard and I got some wrong so they got easy but I think I'd done well enough to get a decent quant score.

The last thing I have to say that helped is getting enough sleep, eating well, and relaxing beforehand.  A friend told me that it didn't matter how I did - that I already had a great life and proof that I was smart and successful.  But I'll tell you what, getting a higher score than I had even hoped for was a feeling I'll never forget.

Good luck!

Amazon.com: Kaplan GMAT 800, 2006-2007 (Kaplan Gmat 800): Books: Eric Goodman