Hi jimzhang93,
In your last sentence, you appear to pinpoint the 'issue' that you're facing - you make 'a lot of careless mistakes.'
At higher scoring levels, the GMAT becomes really 'sensitive' to little mistakes - if you make too many, then a 760 will simply be impossible to achieve. So your immediate 'next step' is to DEFINE the specific errors that you make so that you can work to fix them. The solutions to these types of issues almost always require 'steps' and commitment to working a certain way, on every question (take notes, on the pad, EVERY TIME - don't do work 'in your head', etc.).
All things being equal, a 730/740 score would be an outstanding performance on the actual GMAT, but it sounds like you haven't taken the Official GMAT yet. Is that the case?
1) When are you planning to take the GMAT?
2) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich