Another one that should be no surprise to many -
File cards - short bristled brushes - are great for larger hand files, but not much good on smaller files, say, 4" or so. To clean them, take a piece of copper (or brass) and push it diagonally across the file in the direction the teeth were cut. The copper will conform to the file teeth and shove out any little bits of embedded material.
Round files are more of a pain than flat - you need to follow the contour of the file too.