As you probably know, the FAFSA (Free Application for Federal Student Aid) will be available in January, either at your high school or online at http://www.fafsa.ed.gov/ . As the FAFSA is free, there is no need to use the "pay to play" fafsa.com site.
Every student (why should you bother?) attending college next year should be completing this, and it should be done in January or very soon thereafter.
When you complete it, you'll be using a lot of the same information you use to complete your tax returns. You can even estimate if you have to and make revisions online later. Bottom line: it's one less thing to worry about once it's done.