You can do it. I did the gmat in October and after doing one prep course and getting 500 to 550 on 3 practice tests I went in completely unprepared and scored a 480 ouch...it hurt my ego.

I revamped my study methods and went back on dec 1 and scored a 630. For some people here that is a poor score but I was so ecstatic I almost let a savage scream out while others were still writing...when I got in my car I yelled like a nut case.

Anyway, here is what I did.

1. Math Math Math - I went back to fundamentals and made sure I understood the basics of number properties and re-learned the theory behind all the concepts - one at a time.

2. I did the same for verbal - understood the basics before even trying any practice questions.

3. DO Hundreds of practice questions in the same category until your success rate improves. Focus on one category at a time CR, SC, P..etc

4. Do a practice test a day for at least 15 days in a row.

5. Get a private tutor to review the questions you got wrong. I found a younger guy about 24 - math wiz - who charged me 20$ hour. good deal compared to the standard - but he was a little younger and helped out with his own little tricks.

6. Know all the instructions before writing the exam and use the instruction reading time to breath, structure your essays, and regurgitate any math formulas you need on your scratch pad before the exam starts.

7. Other random stuff I did before my exam - exercised lightly between study sessions, ate like a champion - no matter the cost, abstained from GMAT for a full week before writing and last, visualized myself - over and over - leaving the test building with the score I was aiming for.

Those are my tips
gluck