Organize your books by color:
Pull everything off your shelf and group your books according to color. The order in which you put the colors is totally up to you. Just have fun with your shelves until you like the way they look.
Organize your books in alphabetical order:
You can do this according to the author's last name or the name of the book. Pull all of the books off the shelf, and start laying piles from A to Z.
Organize your books according to genre:
Pull your books down and begin separating them according to their genre. I like to separate children's and adult's books, and then group by genre.