Fill out a free application for Federal Student Aid. Nearly all college scholarships require a FAFSA form to be considered. The form is relatively quick and easy to complete and can be found at FAFSA.ed.gov.
Take the Preliminary SAT/National Merit Scholarship Qualifying Test (PSAT/NMSQT), ideally at the end of your junior year of high school. Many national and local scholarships consider applicants based on their scores on this test and many colleges will not consider students that have not taken this test.
Check with others in your area for those who have applied for and obtained local scholarships. This may include any advisers or teachers who may have records covering other students with whom they've worked in the past and may have valuable information on.
Search the Internet for local scholarships for which you may qualify. The Internet has changed the process of finding scholarships enormously, and made it far easier. According to Scholarships.com, what was once a long process involving finding others who'd received scholarships and tracking down the organization that granted to scholarships has been replaced by a simple Web-search. The College Resources link below contains information on finding scholarships over the Internet.
Apply to as many scholarships as you can find that you qualify for. The applications are generally similar and quickly completed, and the more scholarships you apply for, the more you are likely to receive.