The life of a character should be an unbroken line of events and emotions, but a play only gives us a few moments on that line - we must create the rest to portray a convincing life.
When you're playing a character who's cruel, look for the places where he's kind. When you're playing a character who is unhappy, look for the places where he has a glint of merriment.
The character has to have some kind of arch. The character has to go through an event, and be changed by the human event.
Don't go so deep in yourself that you no longer exist for your partner and for the character and for the play.
