Have so many books that you don't know what to do with them all?

It's hard to get anything done if you can't find your stuff. And, contrary to popular belief, you don't have to be a librarian to keep your books organized. Here's a way to make your books easier to find and avoid having them fall down from the shelf.

[edit] Steps

Pull the books, papers, etc., off the shelf. Divide the items into two piles: those you want to keep and those you want to give away.
Take out any extra papers such as bookmarks that may be in the book. Recycle the unneeded papers.
Make a pile of books that need to be fixed. Later you can decide if it's worth the effort to fix the book or if you'd rather just replace it with a better copy.
If you have any books that you think might be of value, try looking them up on Bookscouter.com to see if anybody is willing to buy them.
Box up your unwanted books. Call your local used bookstores and find out if they buy books. Most thrift stores will also accept book donations, and you can get a receipt for a tax deduction, but don't donate trashed or smelly books, which the thrift store will then have to throw away! You can also give away your books anonymously at your work or school. Book Crossing is a community of people who enjoy giving away their books. Paperbacks can often be recycled (check with your local garbage company), but the glue in hardcovers makes them unrecyclable, so do the right thing and throw trashed books away yourself.
Wipe down the shelves thoroughly with an all-purpose cleaning spray or furniture polish. You might not get another chance to do this for a long time.
With a little work, your books can look this neat.

Decide how you are going to organize your collection. There are many ways you can choose to arrange your books: by size, by color, by number of pages, by subject, by your favorite titles, by publisher, by publication date, by date you received the book, by your favorite genre and then by author, by author (fiction) or Dewey Decimal system/Library of Congress Classification system (non-fiction) or by reading level or lexile.
Make labels for your book using a hand-held label maker to add letters or Dewey Decimal numbers to the spines of books.
Put the books back into the bookshelf in whatever order you decided earlier, and enjoy your clean, organized bookshelf!

[edit] Tips

Adjust these guidelines to reflect your own personality and the quirks of your collection. It's your collection, so organize it in a way you enjoy and can use comfortably. You aren't stuck with it in any case, and you can rearrange your collection as often as you like.
Put larger books, like textbooks, cookbooks, and picture books on a lower shelf to keep them from toppling onto someone's head.
If you organize your books by type, start with the general book type and then split it into subgroups. For example, cookbooks can be organized by cuisine type: Italian, French, Thai, Mexican, etc. Fiction can be organized strictly by author, or you can sort into genre, such as sci-fi, romance, mysteries, or historical fiction. Subtopics can be as specific as vegetarian Mexican cooking or British romance novels. Children's books can be organized by age level.
If you want a more formal catalog system, LibraryThing can be used to organize your books online while keeping track of people who read the same things you are. Some users like to organize by tags; LibraryThing also provides Dewey Decimal numbers, Library of Congress Subject Headings and so forth.
Consider using computer software to organize and track your book collection. For Macs, check out Delicious Library at http://www.delicious-monster.com. With Windows, have a look at MediaMan http://www.imediaman.com. There is also Freeware book management software such as http://www.spacejock.com/BookDB_Version.html, and even full Library Automation packages. Search on Google using the search phrase "Free Library Automation Software."
Dewey Decimal and Library of Congress numbers are usually found in the front of the books with the publication information. If a book doesn't list the Dewey Decimal number, go the the website for a major public library that uses the Dewey Decimal System (such as the New York Public Library) and search for the book by author or title. If that fails, use a subject search to find similar books and use their number.
A useful tool could be the freeware program AZZ Cardfile. One of the free downloads for this program is the Dewey Decimal System. Take a look at the program and the downloads: http://www.azzcardfile.com .
If you are a current student, organizing your collection may spill into organizing your school books, so you may want to make sure your dictionary, thesaurus and other reference books are right by your computer for when you are working on reports.
For home libraries, alphabetizing is probably the best option.