Get to know the blade. Put on gloves and safety goggles before you start, then secure one handle of your shears in a table vise. With a coarse, bastard-cut mill file in hand, “inspect the blade for the factory edge—the manufacturer’s original cut.”
No quick movements. Setting the file at the angle of the factory edge, begin pulling the file along the blade edge in long, smooth strokes in the direction of the blade’s tip. Repeat several times or more, until the blade can slice cleanly through a sheet of printer paper.
Smooth and oil. Use a honing stone to remove burrs on the flat side of the blade, then repeat the entire process with the second blade. “A stone not only smooths the blade but also prevents it from quickly dulling again.” Finish by wiping a bit of oil on the blades to prevent rust.
Source: Men’s Health