The Joy of Less: A Minimalist Guide to Declutter, Organize, and Simplify by Francine Jay
The Joy of Less is the third book I've read on decluttering as of late, and it ranks second in helpfulness. Marie Kondo's book ranks first. (I read that one a couple of times and put it into practice. I appreciate her quirkiness and whimsy.)
I appreciated Jay's very organized and structured approach to decluttering. She provides a helpful guide to how to approach each room.
If you're looking to start decluttering, this is a great place to start.