Use tackle commensurate with the size of fish. If its too light the fish can become stressed. Get the fish into the bank as quickly as possible. Barbless single hooks cause less damage. Or crush the barbs down.
Micro barbs work well.
Carry forceps or pliers to remove hooks. Try not to remove a fish from water. If removed from water support the body of the fish. Do not hold salmon up by the tail if it is to be returned as this can break the spine. Try not to touch the gills - they are very sensitive.