Get rid of anything you haven't used in over a year. Yes, that includes the 1985 edition of "The Art of War" you bought at the library sale. We won't judge you (much).
But don't get too attached, because it's time to face the music. Literally. RIP Your Music Library
Group similar items together. This will help you find what you're looking for, and what's looking for a new home. Like that one vase you bought in 2007 that's been sitting on the shelf ever since. Finding What You Never Looked For
Use those fancy storage bins and baskets to keep your items in order. Don't forget to label them, or you'll just end up with more clutter. Labels Are Your Friend