Use post-it note labels
I don't like the thought of wasting tons of folders, which would happen if I made a new folder with a permanent label every time something came up. As a matter of fact, that used to be a mental stumbling block for me, and I would keep papers in piles while I tried to design filing systems.
So for the past year or so, I've used post-it notes: I grab a folder and take a post-it note, and at the top of the post-it, on the front (oppposite the sticky side) I write a folder title. Then I put the post-it on the folder so the top shows the label space (the tab) and the rest of the post-it hangs down in the folder. That way I know I can easily re-use the folder as my needs change. The post-it's stay on for a long time, have never had a problem with them falling off, and if I wanted to I could use the super-sticky post-its and they would be even more semi-permanent. I bought a pack of the Avery removable file labels but I don't like having to grab a folder _and_ grab a label -- the post-it's are everywhere and always at hand, and I feel happy to be organizing, concentrating on that process rather getting caught up in the labelling process (maybe I get distracted too easily or have trouble concentrating) and I like using the post-its--I buy so many and don't really have that many uses for them, so it's good to have another use. And there are lots of colors to use for color-coding, too, though I don't do that myself.
I just hate re-using folders--if you pull off the label, it ruins the folder. I've tried putting new labels over the old ones, but either the old label shows through or it just looks messy. And I like to be able to combine or re-name or re-classify, and the post-its make that easy and I don't have to worry about wasting folders.
I use end-tab folders for my client folders, with the alpha coding, etc, and I do those up right so they will be organized and easy to find on the shelves. But for reference files and temporary files, and internal forms, and other personal and business filing, I prefer the post-it note labels. If I decide something needs to be saved permanently, I can use standard file labels, and file them permanently (where I generally never see them again). But for getting things on my desk and nearby organized cost-effectively and quickly and helping me to get it done and move on, the post-it note labels have really set my mind at ease and made me comfortable.