Use wooden blocks in a bench-mounted vise. Get a small flat file (6" flat mill bastard) and a four inch "ignition file." It's a good idea to have another screw that's in prime condition for use as a reference.
Work on the worst tooth first. The outside round radius isn't super important, but make sure that it doesn't have any burrs. The vertical part of the tooth should be free of burrs as well, but make sure to keep the beveled edge intact and trending inward. This should be sharpened inward to crush and force the ice shavings inside the screw. Your goal is to restore the teeth to their original shape, with the tips in the same plane. Remove as little material as possible and avoid removing the radius in the corner. Touch up any burrs on the threads and pay particular attention to the starting thread. Finally, give the inside diameter a quick shot of WD-40.
Always dry your screws with the protective caps removed and use the caps for transit.