A jail should be a hotel with good services including entertainment in keeping with the idea that the person is presumed innocent until convicted. The custodial agency should be independent of the police or the prosecutor, and these agencies should have no access to the prisoner if he doesn't want to see them. The prisoner should have full rights of private communication with anyone including the right to use ciphers. Any exception should be based on a court order. It is not clear that our society can afford this reform yet since the police depend on control of prisoners for much of their evidence.
Every institution including a prison develops a tradition.
In the case of a prison, this tradition is usually one of cynicism, despair, individual selfishness and gang rule. Attempts by reformers to make other attitudes dominant sometimes have success in new institutions with selected inmates and young, enthusiastic personnel, but eventually cynicism among the inmates and personnel reestablishes itself and is almost impossible to overcome. This effect can be mitigated by running prisons as batch processing rather than continuous institutions. The idea is that a group of prisoners who will be released at about the same time should be kept together and isolated from others. The staff will attempt to establish a good tradition in this group.