Organizing piano music can be a challenge since the majority of the book spines are so small that the title/color of the book isn't obvious when they are stacked on a bookshelf. I use these handy circle dots to color code all of my music by levels that correspond with the colors of the Hal Leonard method books I began teaching with (Level 1 Blue, Level 2 Purple, etc.). The colored dots "move up" the spine of the book as the level of difficulty of the music increases. For books with various levels of pieces I add multiple stickers. This has come in handy not only when I'm trying to locate a specific book, but also when I need a quick sightreading piece that is a level below a student's current playing abilities.
I also add a sticky name/address label on the back of all the music in my studio library to distinguish it from my students books and help them remember to return it to me.
I have loved the sticker color coded system with piano books so much, I decided to organize our children's books with stickers too. I chose different colors for nonfiction books, Accelerated Reader Books, Board Books, Early Readers, etc. It makes it a lot easier to find a particular book, and when my kids put them away they just have to look at the colored sticker on the spine to find where it goes on the shelf.