I know it's been said before but the thing you need to do most is practice! It's all about being familiar and comfortable with the what the GMAT is gonna ask you and being able to do it under test conditions.
The PowerPrep from PearsonVue is the most accurate of all the prep materials. You get 2 practice tests. My suggestion: learn the basics of the test study for a week or so and take 1. Then use some prep material and then take the second close to your actual test date so you can measure your progress. But make sure to leave enough time to fix your weaknesses.
This is what I used to prepare:
2004 w/CD: very good tool. The book is good for reference but the CD is great. Take the diagnostic to see where you are, then you can devise a custom study plan. I opted to do all the lessons, quizes and tests. Lessons are interactive and give you the basics. Quizes are good for gaging your understanding. Tests are realistic, adaptive and similar to the real thing. Be aware! scores are artificially low so don't be discouraged. For the ~$30 it is very cost effective and much, much cheaper than the thousands they ask for the course - even though the material is almost identical. Only thing missing is good combination/permutation lessons.
Test 1: 570
Test 2: 540
Test 3: 660
Test 4: 640
I felt I needed more practice so I signed up for 800score as well and went through it's course as well. It had some useful material not in the Kaplan
- especially regarding essays and comb/probability questions. Tests are adaptive but questions not as similar to the real thing as Kaplan
or Princeton Review
Test 1: 680
Test 2: 670
Test 3: 690
I wanted more math so I paid for the Challenges offered by GMAT club. The questions weren't always like what you'd find on the real thing - mostly harder, but they definitely get you thinking. Good mental workout. If you want a higher score on the quant make sure you check out the Comb/Probability sections in the Forum - very helpful!
Took the Princeton Review
free test online - 710
One thing I definitely recommend is to take their essays and use the grading service - only $6.99 for two essays. Very useful for gaging your essay readiness. I started my essay prep a week before and did one of each type every day and followed the formulas given by 800score and Kaplan
Be warned, no water, drinks or food allowed in the test center. This threw me off because I'm used to having a bottle of water to sip on while I took the practice tests. Also, I would drink a little tea to stay alert towards the end and couldn't do that on test day.
Test was exactly like the PowerPrep. Got a 730 on both of those.
Week before the test I took a practice test every other day at the same time as the actual test time to get used to getting up early and to build my stamina. I know it's not practical for everyone but it definitely helps. Did nothing the day before but relax and get a good night's sleep.
Actual test - was hoping to do a little better on the verbal. I'm convinced I got a couple questions with no correct answer, wish there was a way to check. But maybe I'm just griping for small things.
Anyway, gotta thank GMATclub for this wonderful site and all the help it provided. Thanks guys!