Who are the actors and what do they act? Playing the part of course can also apply to characters who are not all they seem to be. In my case, Brankaresh, the dodgy Chief Wizard, is a good example of this. But what do your characters pretend to be, where this is the case, and why are they doing it? Who are they trying to deceive and why? The motivation/potential gain must be strong enough to sustain this.
Eileen, my awkward-as-they-come fairy godmother, wouldn't dream of playing a part. She is a good case of what you see is what you get. Which of your characters do this? What drives them to be fundamentally honest? Have they ever been tempted to do otherwise and how did they resist that temptation?
All good things to think about - and there must be several short stories in answering these.