When should I fill out FAFSA?
Most colleges have a specific priority FAFSA deadline. It's a good idea to fill out the FAFSA as soon as you or your parents file a tax return. You can also file with the information from the previous years tax return and then make corrections/adjustments later on.
Totally agree with Linsey here. Check out your college's academic calendar and they usually post there or on their financial aid site what the date is for completion of the FAFSA application. Try to complete it at least a month prior to that date and you should be set to go!