Study hard in college. Admissions committees like to see good grades.
Prepare well for the Graduate Record Examinations (GRE) (see Related eHows).
Form good relationships with your professors (see Related eHows): Visit office hours regularly and keep in touch. Recommendation letters are a vital part of any graduate school application.
Contact your professors as soon as you know you'll need recommendation letters from them. Provide them with addressed, stamped envelopes for the letters.
Research the work done by the professors at the schools to which you're applying.
Contact those professors, and mention their work. Not only will you ingratiate yourself, but the professor will also remember you better if he or she can put a voice - or better yet a face - to an application.
Talk to current graduate students where you're applying; they may have some helpful tips for you.
Keep track of all your deadlines and be sure to meet them all.