I borrowed this list from So Haute for a swift overview of Marie's decluttering and organizing principles:
1. Do tackle everything all at once. Instead of organizing little by little, take everything out and sort it all in one fell swoop, category by category. Save sentimental items for last. Devote an entire day to this if you need to but it’s important to eliminate the excess before you begin storing things away, otherwise you will rebound and be right back to living with a cluttered mess.
2. Don’t keep anything that doesn’t “spark joy.” This philosophy is the core of the Kon Mari Method. As you’re sorting your items, focus more on what to keep rather than what to get rid of. Touch each one and think about whether or not it sparks joy. Keep only the items that spark joy and anything else should go. Only few of our belongings are truly necessary.
3. Do banish all paper clutter. Most of the paper that comes into our homes is never truly necessary. Kondo’s rule of thumb when it comes to sorting papers? Get rid of everything. Obviously, you don’t want to throw away the deed to your house, but most papers, especially anything that can be accessed online are not necessary.
4. Don’t hang on to unread books. When it comes to unread books that are siting around collecting dust, get rid of them because presumably, you’ll never ever read them. The more time that has passed since you acquired the book, the less likely you are to ever read it. (This is something I am totally guilty of! edit: I don't I have an e-reader!)
5. Do strive for simplicity in storage. You should be able to see everything you own at a glance which is the secret to an uncluttered space. Designate a place for everything and try to store as many items as possible in drawers. Never stack things on top of one another and treat every item with respect – no balling up those clothes!
6. Do organize clothes by color. Hang your clothes with like items grouped together by color from dark to light items arranged from left to right. If your items are in a drawer, use this same color coding approach. (edit: and fold! like a pro!)
7. Don’t waste money on organizational solutions. Buying tools and accessories to help you stay organized only brings more stuff into your home and encourages you to store more unnecessary things. The key to the KonMari method is to simplify your belongings as much as possible.
Here's also a great interview with Marie at Luckyshops.