The way to organize them is up to you; I personally prefer going alphabetical by author. You can also go bookstore style and take advantage of interesting cover art by facing a few books out (Image 2).
Now, most of us won't need the insane amount of shelving seen in Image 4, but if you have more books than your space can handle, consider a purge. I hate to get rid of books, but Sarah has some helpful ideas for decluttering your bookshelves.
MORE BOOKSHELVES ON APARTMENT THERAPY
• Wall-Mounted Bookshelves in Real-Life Spaces
• Inspiration: Walls of Bookshelves
• Painted Bookshelves
• 4 Tips to Eye-Catching Bookshelves
• Ariel's DIY Bookshelf Surprise
Images: 1. Design*Sponge 2. Lonny 3. The Estate of Things 4. The Selby 5. Freunde von Freuden 6. Mat Sanders for Apartment Therapy 7. Plastolux 8. New York Social Diary 9. Elle Decor 10. Design*Sponge via I Suwannee