The top qualifications colleges want to see from high school students are strong grades in rigorous courses, so your first priority is to lay the groundwork for a good year. Think about your fall goals, and whether your time management and study skills need some work. (Students in the Class of 2021 can enroll in these monthly study skills classes on Capitol Hill.)
Of course, your grades are not all colleges are interested in. Now that school sports seasons and clubs are starting back up, think about taking a more active role in those that are most important to you, keeping in mind that colleges want to see commitment over quantity. If your extracurricular list needs to be rounded out, consider getting involved with a community organization. In honor of the 9/11 National Day of Service next week, many groups are holding events where you can lend a hand and learn about the work they do year-round. Also make sure to update your resume with summer and fall activities or, if you prefer, create a profile and enter them straight into the Common Application or the Coalition Application.
You should also check in with your school counselor, who may suggest some colleges for you to research. I recommend juniors start visiting campuses in the fall to keep from being over-scheduled in the spring. Check with your family to find good dates for travel or schedule some tours locally to get your feet wet. You can also take advantage of upcoming college fairs and visits college representatives make to your high school. These face-to-face meetings are a great opportunity to talk to the admissions official who may be reading your application later. Attending also demonstrates your interest in particular schools, which some admissions offices track and can count in your favor.