There's a thread on this in the Archives, but darned if I can recall the title. A brief reprise...
After ensuring the shotgun is EMPTY, work it while watching TV, just holding down the slide release and pumping slowly. When arms tire, switch to the other side and go on.
Disassemble to the point where the forearm assembly and action bars are off the action. Check for straightness, then radius the corners of the bars. Use a hard Arkansas stone or a crockstick, remove just enough metal to be visible. Polish where the bars are shiny,then clean and lube with your lube of choice. Reassemble, pump, and note the difference.
Then work polish further by shooting same.
Enjoy...