Get a car organizer. There are types that fit on the backs of your seats or in your trunk.
Into painting? Sports? Knitting? Organize all the stuff related to your hobbies. We say, “Use whatever works” to keep things organized, from shelves and plastic bins to shoeboxes or buckets.
Take time and organize your digital photos. Open an account with Flickr, Shutterfly or Photobucket and start storing photos there.
Download a password manager like LastPass and use it to keep track of all those passwords!
Remove unused apps from your phone.
Donate old books, throw away old magazines.