Determine whether an item should be sold:
My rule is if I haven’t used something for 6 months or more, it should go to someone else that will make good use of it. I am constantly trying new things, and sometimes that means acquiring “stuff”. So getting rid of of “old stuff” has to keep up with my acquisition.
Where to sell all these things?
It always helps to cross-list in multiple places, you just never know where the right audience may be hunting for a good deal. I usually cross-list my items on Auction Sites, Local Classified Websites/Apps, Forums, and through personal network (if I happen to know someone would be interested). Certain category of items work better on one platform or another. And there are category-specific avenue to sell certain items (e.g., musical instrument, sporting gear).