This book is fantastic. I hesitate to recommend it to people who aren't organizing freaks like I am, but it's so genuinely helpful in creating a more pleasant environment that I think everyone should read it. This book is not about cleaning, and not really about decluttering. It's about learning how to tell what sparks joy for you and what does not, and being intentional about surrounding yourself with things that spark joy, and getting rid of everything else. It contradicts other advice to keep what is useful or necessary, and says that you should keep what you love, even if it's frivolous. In the end you are left with a house full of what you love.
Marie claims that out of her clients who have completed the program, she has not had a single one backslide. She also says that people typically go one room at a time, and sort items by location. Instead, she says to sort items by category, gathering them all into one location so that you can see how many you have, and can compare which you love, which you love a little, which you dislike, etc. Then you sort them into piles, and then you organize what you are keeping. Marie says to do clothing first, because it is easier to tell how you feel about it, then books, then papers, then everything else, saving sentimental items for the very last. Once you've done everything else, you will be able to handle sorting your mementos without getting stuck.
The process is simple, and I've noticed that a lot of people are trying to do it without reading her book. If you do this, you are missing out! There are so many little details and ideas in her book that help to change your mindset and prepare you for sorting your belongings and creating the home that you want. This is one of those books that I think I will read again every few years, discovering something new each time.