You can apply vaseline (petroleum jelly) before putting on socks. Nighttime is a good time to do this.
You need to keep them moisturized (not overly so). Use some intensive care type lotion when you're not going to have to put socks right over it. Don't walk around in flip-flops or sandals as that dries them out severely and adds callous. You can try getting a pedicure if they're not sore as they'll use a pumice stone to help get off some of the dead skin and smooth it out. Alternatively, you can soak your feet in epsom salt and warm water and then use a wet pumice stone yourself at home.