Hi ankykool,
When you say that you took one GMAT Test, do you mean a practice CAT Test or the Official GMAT? Raising a 300 to a 550+ will likely take at least another 3 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections (so you will need to work on more than just your Critical Reasoning skills). 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?
2) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores for each)?
3) How long ago did you take this Test (the one in which you scored 300)?
Goals:
4) When are you planning to (re)take the GMAT?
5) When are you planning to apply to Business School?
6) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich