Add yourself to the course waitlist. If someone drops you will be invited to register for the course.
Undergraduate students are ranked on the waitlist based on a point system. Students who are graduating within the next year 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.