These are the mistakes I made when preparing for GMAT.
1. I gave importance to quantity of questions rather than quality of questions. I felt practicing more and more questions every day would improve my knowledge and accuracy.
correct approach: If ur study session lasts 30 min, you must spend greater than 30 min reviewing them( review the correct ones too..you might find an easier way to solve the problem)
2. Take full length GMAT tests including the AWA section. If you are skipping the AWA section, you are making the biggest mistake..you are making a mistake that will cost you > $250 . GMAT is a marathon!!
correct approach: Dont skip AWA during the mock tests that you take. Taking on GMAT verbal after 1.5 hrs is very different from taking it after 2.5 hrs.
Will continue to update this post...lots more to come from my own exp and from what i have read