Marie Kondo's The Life-Changing Magic of Tidying Up is a good book. Its key points are simple and true. As with most self-help books, it is heavily padded with anecdotes and permutations of her central message, though in this case it's still a short and enjoyable book.
The central premise of Ms. Kondo's method is that organizing ("tidying up") is harder the more stuff you have. With lots of stuff, tidying is not just time-consuming but demoralizing. So -- and here is what I assume is unique about her method -- tidying has to start with getting rid of stuff.
What stuff do you get rid of? Everything is fair game for discarding; you keep what "sparks joy." (This is also a unique feature of her method, I believe.) At first I thought that was stupid new-age bullshit. But she's right. Other criteria won't work. Keeping something because you paid lots of money for it isn't going to get you that money back. Keeping something because you might use it one day isn't realistic either. And keeping something because you "want" it is too vague.
How do you get rid of that which doesn't spark joy? In one fell sweep. In Kondo's method, tidying is a special event, not something you commit to for the rest of your life (because that's a very off-putting way to approach anything). After this one special tidying event, after you're organized, all you will have to do is put stuff in its proper place when you're done using it for the day -- and this barely qualifies as tidying.
The rest of the book delves into how to apply the method and how best to organize things once you've tidied (she recommends shoe boxes and a special folding method). How much this matters to you will depend on your particular situation.
I found the book to contain few new ideas -- I'm a minimalist by nature -- but it did inspire me to take another look at my belongings, to decide what else I could do without. In fact, her enthusiasm was so infectious that I got out of bed at 2 AM to do this. So much for the book being a relaxing bedtime read.
P.S. I would add that getting rid of stuff you don't use should also be seen as an ethical imperative. Donating helps out the less fortunate and reduces environmentally-destructive consumption.