I'd like to agree with David Mullen and underline that a cinematographer is at the core a photographer. You should be taking still photos (not with an automatic camera) and trying to keep a little logbook about each image (lens data, film, lighting conditions, exposure, etc.).
Look at photos, paintings, comic books and MOVIES, MOVIES, MOVIES!!!!!!!!!!
Read everything you can get your hands on. EVERYTHING!!!!!!!!!!!!!!
Make little movies on super8, 16, dv, whatever and look at your results objectively.
Get a summer job in a camera or lighting rental company - even if it's just sweeping the floors, you'll have low pressure hands-on experience and will be meeting people.
Cheers,
Dan