“‘Nobody knows how a theatre season is made,’ Paul Miller says cheerily. There is no rule book, no key to artistic or box-office success. Still, nothing made Miller, the artistic director of the resurgent Orange Tree theatre in Richmond, more chuffed than a recent compliment from a fellow director, Ellen McDougall. She said she would recognise an Orange Tree season at a glance, even if the theatre’s name was omitted. So, what gives a programme coherence?”