Just hang back and hope she/him noticed you.
Follow her/him home and learn everything about her possible. DUH!
Go up to her/him, ask him/her out, and get upset if she/him doesn't call you back.
Look at her and follow her/him from class to class.
Follow her from a distance and make sure she/he doesn't notice you.
You try to catch her/his attention and hope she/he notices you!