Have a good long soak in a warm bath, with a good moisturizing bath product - Dove make some great ones. When your feet are nice and pruney, give the rough bits a good rubbing with a pumice stone and make sure you dry between your toes.

Once your feet are dry, rub more moisturizer in and buff with a soft cloth.

I wear sandals every day and have a similar problem with my heels, big toes and the ball of my foot. A good soak once a week and a rub down with a damp edition of the Sporting Life works a treat.

LTS