Hi shivangisingh711,
A 510 is a decent 'baseline' score (the average score on the Official GMAT hovers around 540-550 most years). While you have a lot of work to do to improve to 680+ range, you've given yourself plenty of time to succeed.
Beyond doing lots of practice problems though, you probably need consistent, professional guidance, so that you can learn all of the patterns, tactics and 'secrets' of the GMAT (without having to try to figure out all of that stuff on your own). You would likely find it beneficial to invest in a GMAT Course of some kind (either Guided Self-Study or Instructor-Led). Most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it. We have a variety of those resources at out site (
www.empowergmat.com). I suggest that you take advantage of all of them then choose the one that best matches your personality, timeline and budget.
Have you scheduled your Official GMAT yet?
When are you planning to apply to Business School?
Do you know which Schools you are planning to apply to?
GMAT assassins aren't born, they're made,
Rich