What is the best way to get rid of a callus?

Can be difficult. Calluses are due to pressure against a bone. Depending on where the callus is located somethimes a particular shoe is causing excessive pressure at the callus spot so you may want to stop using it. You can also use a pumice stone to reduce the callus. I do not recommend the otc callus removers from the store. The other choice is surgical consideration to reduce the underlying bone.
Depends on the cause. Many things can cause calluses. Some reasons that one may develop a callus include: viral infections (warts), friction, pressure, repedetive trauma, and a limitation of joint motion. Some genetic conditions may also cause people to develop calluses on the hands and the feet. Treatment depends on the cause of the problem. Have it evaluated by a professional and get the appropriate treatment.