Yesterday, I turned around all the hangers in my closet so that they face the wrong way. The plan is that after I wear an item and clean it, it'll get hung back on a hanger turned around the usual way. By this time next year, I'll know what hasn't been worn at all, and that'll help me decide which clothes need to go.
I don't have many things in my closet that have never been worn (I usually wear new things the same week I get them because I'm excited about them!). I purge my closets regularly, and for the most part, I'm not very sentimental about things I've bought for myself, so it's not like I never let clothes go. Still, I suspect that I underestimate how long it's been since I've worn something. This way I'll know for sure.
I'm thinking about doing something similar for the kids--maybe put a little highlighter tape on toys and have them remove it when they play with it. If I get really, really, really brave, I might just do that with my handknits too to see if there's something that I don't need to keep. That, though, will take much more thought.