I work in a test prep center tutoring SAT mathematics, so here's what I suggest:
practice, practice, practice
You need to be able to think quick, and not get caught into a one-way path of approaching problems. You need to time yourself and focus on your weaknesses. You need to get used to being able to approach problems from many different angles and quickly and decisively choose which one to utilize.
Don't buy into these expensive programs. I know I won't ever send my kid to one. I never went to one, but yet I'm the teacher.
That's because I sat down for several months and dedicated energy to reading, thinking, and practicing, by myself. These programes (kaplan, princeton, etc) just regurgitate the same sh*t a motivated person could pick up with a $10 SAT book from a used book store.
I bought one book-the 10 real SATs-3 months before the test, of my junior year in highschool, when I was 16. I studied as hard as I could for that time (could have done better), and I scored a 1460 in the end. 760 in the math and 700 in the verbal. Could have gotten an 800 in the math section if I focused on NOT BEING CARELESS EVEN FOR ONE OR TWO QUESTIONS!! This is what seperates the perfect scores at this level. Regardless, I never took the test again because I was going to my state's school anyway and was already accepted.
Get the 10 real SATs and sti down every other day for an hour, and devour it. Find your weaknesses and focus on them. Find your strengths and utilize them.
PREREQUISITE: You konw your fundamentals, i.e., the basics of math and english. If you don't, you need to get your sh*t together fast and review them, THEN practice.