Add yourself to the course waitlist. If someone drops you will be invited to register for the course.
Students in the School of Arts and Sciences ranking on the waitlist will be based on a point system. Students who are graduating within the next year will receive 5 points, seniors 4 points, juniors 3 points, and sophomores 2 points. The more points you have the higher you are on the waitlist. Therefore the spot you are on the waitlist could occasionally change based on the students (and their points) who get on the waitlist after you.