School is an awesome way to spread the word about your services. Do you have any edits put together already? Post em up on facebook, share em with friends, get it known in your school (HS or college) that this is what you do. I helped a friend out at my college with a music video, and it blew up. In that week, i then got 5 requests to film different projects. When you first start, its all about that exposure.
Once you have some experience and can put quality work together, pick up a couple gigs for cheap pay or more if the budget allows (im not trying to start a shitstorm on what to charge/industry standard, just some simple advice). Get a small portfolio of professional edits together (stuff you've put together for clients/your best edits) on your fb/vimeo/youtube and market yourself. ask clients/friends/contacts to pass on your information to anyone interested.
Luckily for me im pretty much the go-to video guy at my school. if only college kids had money... I have gotten an offer to film a big jazz concert put on by a frat next weekend, we'll see how that plays out. good luck and feel free to pm me with any questions