I'm at a place in my life where I have too much stuff. In general I've become very judicious and picky about allowing any new thing to enter my life. But it still happens.
My goal and practice for the next year: for every new thing I allow to come into my life as a possession, I'll get rid of two similar things. And by "thing" I mean tangible personal property items (shoes, cars, pens, etc.), not commodities (like gasoline, milk, wine, etc.), or money. So, if I get a new sweater, two sweaters (or a sweater and a fleece) are going bye-bye -- to Goodwill or elsewhere, not a landfill.
Not going to be real legalistic about it, but I'm hoping the practice will make me more mindful of consumption, and stuff in general, and that it will make it easier to downsize housing when the time comes for that. We'll see how it goes.