We had our 3 kids carefully review all incorrect answers on their real and practice SATs, looking for trends and areas to focus on when studying, as well as strategies to answer questions and utilize time efficiently.
There are many books available which can be used to help boost scores (your school may have books available to borrow for free, as well as your public libraries). Khan academy is excellent for practicing, also, and you can find help with specific areas where you may need to target extra study time.
Rather than spending large chunks of time on full length practice tests, our kids would take timed tests of various sections during the week, whenever they had a little time to squeeze it in, with a couple of full length practice tests when time permitted.
There are lots of ideas and suggestions for books and strategies in the testing forum/threads here on CC, it can be a great resource.
Definitely look into taking the ACT, some students prefer the format and do better than SAT results.