I admit it. I'm a nerd. I like that my spices are alphabetical- makes them easier to grab when the baby is crying and the phone is ringing and the oven timer is beeping. I also like my books arranged alphabetically by author, at least the fiction titles.
My nerdy friend Lisa (she admits it) got me started on taking book organization seriously, and as you know we homeschoolers can amass a lot of books in a short amount of time.
To begin organizing your books, you must know what you have. You can track your library acquisitions using software like Readerware. Next, get serious and label or otherwise mark your books using Dewey's system just like the "real" libraries. This is a fabulous project for a high schooler in your home. Because my kids were little when I started cataloging our books, I made little stickers for the spine of each book that would identify which shelf they should go on (see- told you I'm a nerd). But I have my eye on the 13-year-old and will soon hire him to make labels with the proper Dewey decimals.
After getting everything on the shelves and organized, I then bought tab labels for each shelf. You can get almost anything library-related from Demco.