The first step to do better in quant is to get the basics strong. Tricks will help you only if you know the basics. GMAT tests few concepts in infinite ways. I would suggest this:
1. Identify your weak areas ( Like geometry, number properties etc.)
2. Indentify your strong areas.
3. Work on basics of weak areas WITHOUT IGNORING your strong areas. If you have time then you may use MGMAT math books. (I have not used them, so can't say how useful these will be).
4. Always do problems in timed environment. I am sure most of the peopel can solve most of the problems if time restrictions were not there.
5. Do not spend TOO much time, as people do, on probability. GMAT will ask you only simple, but tricky, probability.
And now comes the most improtant: PRACTICE
. Math is gonna kill you if you are out of touch for a week or so.
SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008