Soaking your feet in warm water for 10 to 20 minutes can soften your feet up and then you can use a pumice stone to remove any dead skin cells which will help smooth the bottom of your feet.
You can help keep your feet soft by applying some Vaseline or Moisturizer to your feet daily before putting your socks and shoes on.
Soak your feet daily in warm water as well to help keep your feet soft and smooth and regularly use a pumice stone to remove the dead skin.
You can also add either regular vinegar to the foot bath or some apple cider vinegar to the foot bath as well and both the apple cider vinegar or regular vinegar will kill any bacteria that could be on your feet and keep your feet soft.