No, do not start studying now! You'll burn through the best prep materials well before you're taking it for "real." For now, just read as much as you can, everything from novels to newspapers. You can also start working on vocabulary - it's good for school in general, and you want to learn new words slowly over time. By the time the SAT rolls around, you'll kick butt on the sentence completions
As for the schedule, students frequently will take the PSAT for the first time in October of their sophomore year. If you don't know already, the PSAT is just a practice for the SAT. You'll take the PSAT again in October of your junior year, and this is when it counts for National Merit qualifying. You'll also take the SAT for the first time in your junior year. Many take it in the fall/winter and/or the spring. You may want to take it a final time in the fall of your senior year.
So hold off on any serious prep for now, and just focus on keeping your grades up. Come back to us in the summer before your junior year to get on track for prep for the real thing. Good luck!