Welcome to the GMAT world !!

Well, it looks like you are particularly struggling with Verbal than with Quants. So my first question is when are you planning to take the exam? A lot of suggestions we give depends on when you are taking the test.

If you are taking the test after 2-3 months,
first month:
start with your high school math book and brush up all the basics (This is really important). Some people get MGMAT Quant strategy guides (5 guides) and brush up quants basics. It is actually expensive in my personal opinion and i find my high school math book really useful. Opinion varies person to person. If you are ready to shell some dollars, then go for MGMAT Quant strategy guides (all 5 guides). It is a well organized book.

For verbal, buy CR strategy book and SC strategy book and study all strategies. I would personally suggest you to buy Powerscore CR book and MGMAT SC guide. If you want to brush up basic grammar, you may wish to look for a suitable book. If you come good with CR strategies, you would possibly come good with RC as well.

2nd - 3rd month:
Practice with OG12, quant and verbal supplements (2nd edition). Practice questions in this forum. You may also get some other book to practice problems to work on later but it is not necessary to think about it right now.

Hi
Thanks a lot for your advices...
I think I'm good enough at math, just have to brush up on it a little, but my Verbal skills are not satisfactory since I'm not a native speaker. Actually I've got plenty of time to get prepared for the test. I'm planning to take it in September 2010. As the Verbal section being the main part of GMAT I need to focus on, I'd like to get some advices about tackling the problems in that part.
I need a study guide for this period. What guide would you follow if you had a lot of time???
Thanks again in advance!