you can take a KAPLAN class, but it might cost you some money. A lot of people have gotten a 200 point and higher difference on their tests after taking this class. Or if your school offers a "mock" SAT, it is like taking an SAT test but it's the old version they don't use anymore, it's good for practice. Or you can buy books about the SAT and it tells you what to study for the most and stuff like that.
In addition to improving general test taking skills (e.g., time management, when to guess vs. not answer a question, etc.), the two areas where test takers can typically improve their SAT (and GRE) scores the most and/or quickest are (a) vocabulary and (b) math word problems. Options to work on these, apart from taking a test preparation course from a commercial vendor or your local community college/university, include trying word search and crossword puzzles, using test prep software (there are many free apps for smartphones for this), and individualized tutoring.