First strip the finish, and scrub and scrub and scrub, with a nail brush and kitchen scouring powder, the checker to get all the crud and oil out.
Make any repairs to any chips or splits, dowel fill and re drill screw holes as necessary. Steam out any Dents as best as you can, sometimes the ones that don't lift can be carefully chiseled out without ruing the lines of the for end.
Then freshen the chequering with the appropriately spaced tool.
If the for end is really battered. If you can get away with it sometimes its better to just scrub it out and re lay out the pattern, however often there is not enough wood in the for end to to that without ruining the shape.
