my highest SAT score was a 1500 - 800 verbal, 700 math (i took it before the test was added the third section, obviously). i did absolutely no preparation, and i think most of the books and courses are a scam. I had a very smart friend that did a TON of private tutoring with Kaplan (one of the main test prep companies) and her score actually went down. taking the test more than once should increase your score anyway, and i think it's hard for those companies to prove that they can make a difference for any given test taker.
i think the best thing you can do for yourself is to understand how the test is graded (if there are penalties for guessing, if a wrong answer deducts points or merely doesn't gain you any, etc.) so that you can make the best choices with the group of questions that you get. don't stress, get a good night's sleep, and eat a good breakfast beforehand since the test is long. remember, if you don't like your score, you can always take it again. i took it twice and got scores in the 1400's before i got my 1500, which i was satisfied with.