Seems to me that your critical reading and writing sections need to improve. This probably indicates you need to improve your vocabulary.
Suggest you read a few articles from the New York Times everyday (www.nytimes.com). Lookup any words you don't understand in a dictionary (www.dictionary.com is good).
If you need vocabulary lists do a quick google search for SAT Vocabulary or something similar there are plenty of free resources out there.
Then do some practice tests for the areas of the SAT you need to improve on:
Try this google search: http://www.google.com/search?q=sat+critical+reading
do the same for the writing section.
Some practice sat writing questions can be found at
http://www.majortests.com/sat/grammar.php
Finally, as shuttupjessmah says - The Official SAT Study guide from the collegeboard is probably the best resource and the first book you should buy.