Help Improving Math PSAT Score?

I'm a sopre and got a 47 on the math section of the PSAT. It's slightly above the national average; but, it's no major improvement over last year's score of 45 and I know that I really need to improve my math abilities on these tests if I want to get a really good score on the actual SAT. Out of all those test prep books (Princeton, Kaplan, Barron's, etc.), which one prepares best for the math section of the SAT?