This is one of a few topics I review with my T each session.
I've committed to decluttering the basement, porch and garage.
I have a terrible time lying -- it's easier for me to get rid of a whole bunch of cardboard boxes than to not do it and lie about it.
Anyway, my approach is to pick up a couple of things to throw away whenever I'm in one of those areas.
I also have the rule about donating old clothes if I bring home new ones. But old shoes get thrown away, and underwear goes into the rag pile.