I’m not a fan of trite organizing advice, but I live by the "one thing in, one thing out" rule. Right now I’m wearing a new pair of boots that came in the mail yesterday, and one pair of old boots that I haven’t worn in probably 4 years is sitting in the foyer, headed to the thrift store.
Nothing enters without something leaving. It’s a reflex triggered as something comes through the front door.
My latest video in the minimalism series illustrates this. It’s a show and tell of a number of things that I donated because something better replaced it. More than a rule or reflex, it’s a lifestyle. To acquire anything without releasing something is to tip your scales in the “How did this place get so cluttered?” direction.