Buy a foot file or pumice stone (should be able to find these in the cosmetic section of any drugstore). In the shower every day, give your feet a good scrubbing with the foot file. Then, while feet are still moist, give them a good slathering with a heavy-duty moisturizer (don't do in between toes, but do soles, heels, and all the crusty bits). Immediately throw some cotton socks on. You can do this daily with your shower, or if you want you can do it twice daily, just soaking your feet first in a bucket of warm water or running them under the tap in the tub.
A week of doing this should make your feet nice and soft. Also works for weight training calluses.