You'll want to scrub the balls, bottoms and sides of your heels and around the toes. To get the most leverage, sit on the side of a bathtub, facing inward. Remember the pedicure motto we read about once, "smooth, don't remove." You'll want to stop if your foot turns bright red (this means you've scrubbed too hard). Remember, that tough skin is there for a reason.
Any basic foot file or pumice stone from your drugstore will do the trick, but if you want the Cadillac of foot files, try a ceramic foot file.