Hi Nandu123,
Based on what you described, it's unclear how you have been studying up to this point. In addition, is that 540 an Official GMAT Score or a practice CAT/mock Score? Before I can offer you the specific advice that you’re looking for, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied? How many hours do you typically study each week?
2) Have you used any other study materials besides the Official Guide?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) When are you planning to take the GMAT?
5) When are you planning to apply to School and what Schools are you interested in?
GMAT assassins aren't born, they're made,
Rich