We should start with first time offenders. Let's remove them from the traditional prison environment and put them in a "foster family" setting. I think many criminals came from broken, dysfunctional families and if we can give them a desire to change before they become hardened criminals, we stand the chance of making productive, honest citizens out of them.
When a person is found guilty of a crime and is held accountable with prison time, prison should be a rehabilitation from the action that put him or her in prison to begin with. Inmates should not have time to sit around and engage in the very activity that landed them in the system i.e gangs, violence, rape, smuggling, it all happens in prison too. Inmates should not have time to be hardened or to learn new crimes. They as well should not have to worry over being harmed by other inmates or guards. It will either toughen you up or mess you up or both, abuse in any form is still abuse and the still of abuse usually ends badly. Prisoners should experience therapy, and self help classes and mental evaluations to determine if rehabilitation is even possible. Inmates need a structured environment that promotes being a better person not a caged animal left to linger with others to do as they please until their time is up. When inmates are hardened to a prison lifestyle not only is the transition back to freedom harder they themselves are more susceptible to going back to prison.
It would be great if the incarceration of a criminal could result in an improvement in his character so that, upon release, he or she could become a productive member of society. The recidivism rate is too high currently and sometimes resembles a revolving door for inmates. I am not sure how it needs to be changed, though, in order to accomplish this improved character. Awhile back I read of a new program that was intended to help heal the wounds that many inmates had from events in their childhood or early adult years. Perhaps if we could figure out why people do the things they do, we could figure out how to steer them in a better direction.
It depends on the individual and the sentence they have received. If someone is in prison for life, then let's just warehouse them off somewhere with the other lifers and provide them with minimal support. Someone who is serving a short sentence deserves better treatment, and the opportunity to improve themselves through rehabilitation programs.
I think it harms both the prisoner and society as a whole if we treat prisoners poorly in prisoner, the convict will feel resentful towards society when they are released and commit another crime out of anger, we should be enforcing positive lessons and opportunities for the prisoner to better himself while in prison so he has a new chance at life on release.