During your junior year, you become eligible to apply for awards like the Truman Scholarship, and you also become more competitive for awards like Goldwater and the Udall. This is the year that you should start applying for the national scholarships that are relevant to your subject area.
You should also be keeping up your grades and continuing your involvement in research and leadership opportunities. You should also begin to think about graduate school.
For more opportunities, check out: Juniors