I want to sign up for the Common Application as a junior so I can get a preview of what it involves and start the planning process. Can I do this? Or do I need to wait until next year?
Yes, you can create an account during your junior year and continue to use it when you apply to colleges your senior fall. Common Application accounts will now roll over most of your responses from one year to the next (this is new for 2016).
"We will preserve the answers you provided to any questions that appear in the six sections of the “Common App” tab: Profile, Family, Education, Testing, Activities, and Writing."
However, this rollover policy doesn't apply to all parts of the application. Things that won't carry over include college-specific questions and writing supplements; release authorizations and FERPA selections; recommender invitations, assignments, and forms; PDFs of Common Applications and Writing Supplements submitted the prior year; responses to any questions that have now been removed; and responses to questions that changed their format from the time when you first answered them. If you filled out any of these items in the application for the previous year, make sure you save your responses somewhere else so you don't lose any of your hard work!