If you use hangers, there’s a really easy way to figure out what you’re not wearing. Take everything in your closet and flip your hangers around (the hanger opening pointing toward you). Once you wear an item, put it back in the closet normally (hanger opening pointing away from you). In six months to one year take the items whose hangers are still pointing backwards and donate them.
I usually post the date I started this experiment somewhere in my closet or leave a reminder on my calendar so I don’t forget to follow-through. After a couple weeks it becomes really obvious which items you’re not using often.
I can’t remember where I first heard this trick, but Oprah’s on board and since it takes two minutes to start the experiment, you should be too.