Your goal is not out of reach. How much time do you have?
You are probably looking into 2 months of study to improve 300 points.
I would recommend you start here if you are not very familiar with the test itself:
gmat-faq-frequently-asked-questions-about-gmat-75809.htmlYou should also get some books - I would recommend that you get a Kaplan Premiere, Kaplan Math Workbook and Kaplan Verbal Workbook and after you are done with those, get Official Guide 12.
You can see more GMAT Books here that will satisfy your wildest desires:
top-gmat-prep-books-guides-reviews-comments-77703.htmlAfter you go through a few books, get yourself a copy of GMAT Prep - here is what it is and where to get it:
gmatprep-gmat-prep-powerprep-power-prep-free-tests-77548.htmlBy the time you are done with Math and Verbal workbooks, start taking full length tests, you can use the GMAT Prep, but also look into other tests:
all-gmat-cat-practice-tests-links-prices-reviews-77460.htmlFinally, check out this "Share your GMAT Experience" forum for some testimonials and reviews of what worked and what did not.
Ask if you have any questions!