Start by cleaning the metal parts of your tools. Use a wire brush or wire-steel pad attached to a power drill.
Lock the tool into a vise and use both hands to move a mill file along the edge of the blade toward the shovel's point.
Flip over the shovel and remove burrs on the back side of the blade with sandpaper. If any rust remains on the blade, remove it with the sandpaper.
Lightly coat the blade with machine oil. Apply several light coats of linseed oil to the handle if it's made of wood. Let the oil soak in the handle after each application.