Stop calluses.
Credit: Photograph by Michael Pirrocco

Stop calluses by using a file like the PedEgg ($10). Rub it back and forth over rough spots, usually the heel and the ball of the foot, until the area of thickness disappears. The file also removes dead skin to prevent thick areas from forming. Whatever you do, though, don't use a pumice stone: They're too porous, and so can become a breeding ground for bacteria.