10 Secrets of the GMAT

1. Time Management is Everything
Everything. It doesn't matter whether you can answer a question correctly; it matters whether you can do so in the time allotted. Finishing each section (i.e., giving yourself enough time to get through all 37 math questions or 41 verbal questions) is crucial to your score.
2. The Last Questions Are As Important As the First
The most persistent myth about the GMAT (and other computer-adaptive tests) is that the first few questions make or break your score. It's not true. Odds are, if you get most of the first five questions wrong, you're not going to get a high score, but that has a lot more to do with your skill level than the algorithm that determines your score.
3. You Don't Need 90th Percentile Scores To Get a 90th Percentile Score
This sounds paradoxical, but it's not. If you score approximately in the 80th percentile of the quantitative section and the 80th percentile of the verbal section, that translates into a 90th percentile or better score. (92nd, last time I checked.)
4. Rates and Ratios Are More Important Than Combinations and Permutations
People obsess about the latter, and test-prep companies enable that obsession. In fact, there are far more questions on the test on "simple" content types like rates, ratios, and percents. The secret: those areas--especially rates--really aren't that simple, and most test-takers don't study them enough. That's why Total GMAT Math includes extensive drills on all of those topics you may have ignored.
5. There Are No "Almost Right" Verbal Choices
Despite the wording of the test's instructions, don't rank verbal answer choices by "most right," "almost right," "sort of right," and so on. There are two possible classifications: "correct" and "incorrect." That's it. On every single verbal GMAT question, four of the answers have something identifiable wrong with them.
6. GMAT Prep Courses Aren't Designed To Get You a 700
Prep courses are designed to appeal to a wide range of students, and that means the content is generally aimed at people whose ceiling is in the 600 range. That doesn't mean you can't go to Kaplan and get a 700 eight weeks later--of course you can. But most of the work that gets you from a 600 to a 700 comes from you, not from what you'll learn in class.
7. You Have Plenty of Scratch Paper
Unless you have huge handwriting (in which case you should work on that), the front and back of six sheets of paper is plenty. Don't stress over it. Worst case scenario, you can raise your hand and the proctor will bring you more. Of all the aspects of your GMAT test experience that should worry you, this is pretty close to the bottom of the list.
8. There Are Lots of Experimental Questions
Depending on who you ask, there are as many as 8-10 experimental questions per section. That's close to one in four. If you needed any more convincing that you should guess on the questions that completely baffle you and save time, this should be it.
9. Science passages Aren't Uniquely Challenging
If you approach them correctly, anyway. You don't really need to learn any science, you just need to catalogue the information you're given and keep track of some differing opinions, just like on any other type of passage.
10. You Don't Need Long Division
The GMAT reliably uses a set of simple numbers. When it doesn't, you can usually approximate. There are few better uses of your study time for the math section than learning some mental math tricks. They will save you time on the exam, and you'll get a better grasp of how numbers "work together" for questions on topics such as factors and multiples.