1. RAISE YOUR STANDARDS
When you buy a new pair of shoes, is there an old pair that you can remove? When you bring home 5 new items of clothing, can you admit that there are probably 5 items in your wardrobe that you just never wear? When you buy a stapler that works so much better than your old one, do you actually pick up the old one and donate it? Or does it stay on your desk collecting dust because it's "still useful"?
Raise your standards on what deserves to be deemed "useful" or "valuable" when it comes to your space and start subtracting whatever doesn't meet YOUR standard.