In regards to improving your math..
-do all of the questions in the Official Guide, review the answers, write down your errors, and a few days later redo the questions you got wrong.
-do all of the math practice tests and math section of the CATs on the Kaplan
CD to improve your timing; don't worry if you fail to finish the practice tests before the time is up. Also review the answers, write down your errors, and a few days later redo the questions you got wrong.
-then do the math problems out of the Official Guide again under time conditions starting from the problems in the back of the book
In regards to the math are you having problems with Data Sufficiency (DS) or Problem Solving? I had a problem with DS when I first started my prep. However, I kept practicing DS questions consistently until I got use to them.
In regards to PS, you may want to check out a college algebra, arithmetic, and geometry book to go over your weak areas while you practice math questions.
The first thing I did before preparing for the GMAT was to flip to the Math Review of the Official Guide to the page that lists the areas that are covered on the GMAT. Likewise, I reviewed those concepts in detail from math books (I checked out at from my local library).
By the way the Princeton Review
Quant was very easy to me; much easier than the real GMAT.