Do very well on your SATs. Retake them as many times as you feel is needed. Don't be afraid to apply for scholarships that seem like a long shot. You can bet on others feeling the same way you do and not applying. There are millions if not billions of dollars that goes unclaimed every year. Another thing, stay very active in school. Community service is a big win right now for scholarships.
Oh and don't worry if you don't get alot now. You can keep applying for scholarships while in college. A month ago I sent in my scholarship packet for my uni. Hopfully I will pick up a few extra bucks.