i've spent a small fortune on prep books and have the same prob - i suck at quant.
after all this time, i finally found what i think is the holy grail of quant prep books - Manhattan GMAT
strategy books. they do an amazing job of breaking down the components of each area and give you a way to build on the basics then apply that to the real thing.
go to the manhattan gmat
website and they have a book store there. the books are $26 each, but are worth much more.
is junk cause it over complicates things. you'll never see half the stuff kaplan
presents in the books on the real thing.