Books can be quite charming. The intangible things that they contain are endlessly fascinating: Ideas, memories, methodologies, data, definitions, style guides, pictures, stories... all these things are definitely worth keeping.
But they pile up quickly.
A few years of careful book collection may eventually create a messy bookshelf. It's important to organize your library of books carefully, or it'll take forever to look up that old quote in your buried Bartlett's.
Getting organized is a matter of picking your favorite theme and pressing that theme upon your own shelves. Melvil Dewey, for example, came up with a great idea in the 1800's; 10 different book classes, grouped together by topic.
This is a great idea if you had a balanced library back in 1850, but modern readers realize that if you have a ton of fiction, it's not so helpful to have several classes devoted to philosophy, social sciences, language, pure science, etc.
If you're too lazy to match a system to your own collection, this website has lots of discussion on classification systems: LibraryThing.com
Readers lucky enough to have a dedicated library (or simply a room stuffed full of books) have a distinct advantage here, but even if you've got a library that would make Colonel Pickering jealous, you'll still need to unpack all the shelves. Ugly, yes, but it's necessary.
A successful book organization scheme entails packing up a few boxes for charity. Buck up, and make some tough choices. Obsolete textbooks (that you despised even at the date of purchase) are a great place to start.
Next up: Anything over 3 years old that relates to computers, board books your teen has outgrown, and any fad-driven corporate management drivel. Be ruthless, and remember, the more books you dump, the easier it will be to reorganize (and make room for the new books).
Do they need reinforcement? Paint? Did somebody lose a fifty? Can you get by with less shelving? Can you consolidate the books into one area?
Notice that all these good questions arise from unpacking all the shelves!
After you're done, your successful book reorganization job will be apparent to everyone, bring the desired book of the moment quickly to hand, and give you some room to breathe. And maybe allow for an extra trip to the bookstore.