Go onto the ADEA website and preview the guidelines for the application. Write out your personal statement, you should have already asked for all your LORs so they can have time to write them, start listing all your extra curriculars, and maybe get a transcript for yourself so you can enter your courses. You don't need to have it done the first day, take a week to make sure everything is the way you want it, but as long as you submit within the first month you will be what I consider early.