Take a prep class. The earlier you start, the better. Think of preparing for the SAT as training for marathon. The more practice and familiarity you build, the more confidence you'll have on test day to go in and score well.

I would take a class. I know some kids in my school who have started prepping since 7th grade.

Some of the math that you learned in 9th grade is relevant to what you'll see on the Math portion of the SAT I test. I would pay attention and do well in Algebra and Pre-Calc to cover that section. For Critical Reading and Writing, try to take full advantage of your English classes to improve upon your grasp of grammar and the language, as a whole. Also, pick up a few books and work on your vocabulary. By starting now and learning 2 new words per day, you could accumulate up to 1200 SAT vocab words by the time your 11th grade year rolls around.

Taking a prep class is always a great idea. Especially since you're starting early, learning about the SAT and what to expect will get you a really good score. Also, a prep class will point out things to pay extra attention to in your classes, since you know they will test it on the SAT. The earlier you start, the better your score will be!