I'm re-reading Keith Johnstone's Impro, again. At first it seems to be a gentle meander through the early days of improv theater sports, but little by little he unveils the powerful tools of status, masks, and improv games all of which help players stop overacting and start being more authentic—and thus more believable and interesting. From an interview:
You should be as obvious as possible. At its heart, your obviousness is unique because it is only obvious to you. In Kafka’s story the Metamorphosis, it is obvious that the character would wake up as a cockroach, because that is how Kafka felt. But, that is not what is obvious to everyone, so it appears creative. You are the only one that thinks you are being obvious.