Well, maybe not quite that early!
Do you want to play a sport in college? If so, you need to plan ahead -- as early as freshman or sophomore year in high school.
Freshmen should be looking at their four-year plan for academics and making sure that they have the rigor needed to be eligible to compete in college. The NCAA has strict requirements for coursework. At a minimum, you will need to take four years of English, three years of mathematics beyond Algebra I, two years of lab science, and two years of social sciences. Most college-bound student-athletes have far more rigor than that!
Sophomores should begin putting together an athletic resume, thinking about the type of schools that they would like to look at, and contacting coaches to set up unofficial visits. They should also take the PSAT and pre-ACT (if offered at their school) to get a sense for where their standardized testing will land. Coaches often ask about grades, rigor, and scores right from the start -- they don't want to waste their time or yours if the student will not make the cut with admissions. For this reason, freshman and sophomore grades are very important!!
Enlist the help of your club coach or high school coach early on as well. Many college coaches will reach out to the coaches that have worked with you in high school to get a sense of the player's coachability, overall attitude, and potential for success.
Finally, research college showcases and camps for the summer. But be careful -- some are just money-makers for the college and offer limited benefit in terms of recruiting. So proceed with caution before spending a lot of money and time.