This topic is a little dated - but after many different tries, I have a perfect filing system in my studio. I just thought I'd share. It actually works in three different ways. I have a standard set of wooden "mail slots" purchased from any office supply store. There are about 24 slots set up in four columns going across, with six slots going down. I have two units stacked on top of each other. This is where I keep my current method material that I hand out regularly. This is also my current inventory - the music lays flat and is sorted by level. It is easy to see if inventory is running low. I have a column for each of four different methods I use - plus some areas reserved for the current Festival selections, or holiday selections if it's that time.
Secondly, I have a tall standard bookcase that is loaded with magazine files. This is where I keep my studio copies and they are sorted alphabetically either by composer name or topic, or method name - however I usually refer to the music. I can quickly find anything that comes to mind.
Thirdly, I have several tall stacks of plastic storage bins the drawer type, clear plastic. This is where everything else goes. So, books I don't use often - or odd collections of material. One drawer is full of various Theory books, another Technique books - the ones that aren't part of my regularly used method material. There is a lot of old music stored here - a hodge podge of sheet music. Even drawers full of prizes, markers, stickers, etc.
I also have another bookcase that holds all other odds and ends in various baskets, files, or loaded on the shelves. New assignment books, folders, certificates - magazines, reference books.
With all of this in place, I am organized and can quickly find what I need. But I made many attempts to get to this point. Hope this helps anyone out there trying to make sense of all their stuff.