The hanger trick is not original but it is so wonderful I want everyone to know about. It is so cool that I hope it inspires you to clean out your clothes closets right now!
After you remove everything from your closet and decide what clothes you want to keep, hang them back in the closet the "wrong"way, with the hanger hook facing forward. When you return something to the closet after you have worn it hang it in the "right" way, with the hook facing the back of the closet.
At the end of the season it is easy to see which clothes to discard - the ones with the wrong way hangers, the ones that had never been worn.
If you want to gain some extra hanging space, try this with your coat closet. Coats are bulky and take up a lot of room and you'll get some space by removing just two. But I am a little more lenient when it comes to discarding coats. They tend to be expensive and you don't want to make a mistake tossing a fabulous raincoat you didn't wear one year because it rained less than the year before. So I have a longer time line for coats: the ones on backwards hooks at the end of the second winter get donated.