Hi alibega,
Raising a 300 to a 700+ will be a challenging task and will require at least 3 months of consistent, guided study (and likely more) - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Thankfully, the GMAT is a consistent, predictable Exam, so you CAN train to score at a higher level. Since you're not planning to apply to Business School until next year, you also have plenty of time to study - which is good.
Given everything that you've described, you would likely benefit from investing in a GMAT Course of some type (either Guided Self-Study or instructor-led), so you should plan to look into the available options. You might also find it worthwhile to learn the 'fundamentals' from some of the books that you already have. 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.
If you have any additional questions, then you can feel free to contact me directly.
GMAT assassins aren't born, they're made,
Rich