One thing I've tried recently and works really well is a sanding buff, mounted in my Dremel. I admit it isn't the most economic means, they seem to wear fairly quickly, but they work really well, easier & faster than cleaning pieces by hand with files, emery boards, sandpaper, etc. Using a low speed on the Dremel and a light touch, even fairly delicate fretwork can be cleaned up with these. If they were a little cheaper or lasted longer, they would be the greatest thing since sliced bread.