This book is a lot longer than it really needs to be. It is however, worth skimming to get someone else's perspective if you're really trying to make an effort to declutter. A lot of it though is just not bringing home things in the first place if they don't spark joy and you have nowhere to keep it or an immediate use.
In summary, does your possession spark joy/make you happy when you see it? If not, move it along. Sort and organize your stuff by type rather than location as you might have one type of thing stored in multiple places (eg; socks. Save and purge them all in one pass).