Don't limit yourself. There are also scholarships for unique talents and abilities. Don't confine yourself to academic scholarships or the big national awards. Small awards will come in handy later on for things like books, toiletries and other college necessities. It's never too soon to start your scholarship search.
Some organizations give college scholarships as early as junior high school.
Focus on deadlines. List the scholarships with the earliest deadlines and give them first priority. Take practice tests in the fall of junior year in high school, then start taking the real tests during the spring of junior year and fall of senior year. Most need-based scholarships require family income and tax forms to prove financial need. Prepare these forms ahead of time to qualify for scholarships.