I'd just take practice tests. If you really want to improve then courses could help (though I had a friend get an 800 on the first sat, and 820 on the second after courses, so it's not guaranteed). Though I didn't study or practice for mine. I jumped from 1100 to 1330. Didn't take math for a year and my math score jumped from 470 to 600. I'm horrible with formulas, but I'm excellent with mental math which helps when I haven't seen something before, and also why I got A's in math until the 8th, after that I failed as often as I passed, since I could no longer do the formulas in my head, or make up my own formulas. I can't figure that one out at all, especially since my two psats were 400 (9th grade) and 500 (early 11th) and one practice one I did in my math class in 11th grade was a 460 (I was also in the lowest math phase). I was pretty consistent up until the last one, and I hadn't done any math in about a year. All I did for math was the day before the SAT's I went on collegeboard.com and started to do a few sample questions, I think I did 4 before I got too bored. My verbal also jumped from 630 to 730.
Just don't get too worked up about the SAT's, they are becoming less and less important unless you are going to the elite schools. They are huge when applying to harvard, brown, MIT, yale etc., but not so much for lower universities. Basically, unless your borderline on getting accepted, they won't really be the deciding factor in most universities.