Guide to avoiding STUPID mistakes on GMAT

Quant:

1. Read questions carefully. Dont assume what they are asking for.
2. If x is defined as a number, not an integer, it can assume a range of values, +ive, -ive and fractions. Very easy to miss this and screw up on DS questions.
3. Understand what '0' is - very important.

Verbal:

1. SC - just because you see a choice which sounds reasonably good, don't stop. Always read all the 5 answer choices and pick the best one.
2. RC - don't worry about assessing the difficulty level of a question. I've seen several posts in multiple forums which assert a direct correlation between question difficulty and your performance on the test. While that is likely the case for any CAT, there are several experimental questions on the test and you will never be able to identify them. Also, what is easy for you may be difficult from GMAC's perspective and vice-versa. Getting a long RC passage only if you doing well is a myth - I took the test twice. In the first instance, where my verbal score was dismal, I got some really tough and long RCs (possible cause for my crash-and-burn performance on that test). The second time, I was getting worried since I was getting questions which all seemed fairly easy (not a single long RC). I scored ~25 percentile points more (93rd percentile) on the second test.
3. Make use of the break(s) - every minute of it. They are there for a reason and there are no extra points awarded for getting done early.
4. CR - be wary of questions that use multiple negatives. Always translate to the simpler form before you work the problem. Also, not weaken doesn't necessarily mean strengthen and vice-versa. For example, "Each of the following statements if true, weakens the argument, except" - means which one of the following does not weaken the argument. The correct answer doesnt necessarily have to strengthen the argument - it can be totally irrelevant as long as it doesnt weaken it.