Put on work gloves to protect your hands while working. Turn the shovel so the front of the blade is easily accessible and the beveled edge is facing upward.
Remove any corrosion, dirt, or debris from the front edge of the spade with a stiff bristle brush. Loosen and brush away as much debris as possible so there will be a clean edge for sharpening.
Brace the spade with one hand and hold the file with your other hand. Hold the wide flat side of the file against the beveled edge of the spade. Adjust the angle of the file so that it matches the angle of the blade bevel.
Start along one end of the beveled edge and push or pull the metal file along the spade edge. Lift the file, return to the starting edge and repeat. Continue making passes across the beveled edge with the file until a honed edge is formed.
Turn the spade over so the opposite side of the beveled edge is accessible. Run the metal file gently along the edge to remove the burr that was formed while sharpening.
Place a few drops of general-purpose oil on a rag. Wipe the newly honed edge of the spade with the oil to help prevent rust and corrosion.