Watching actors rehearse lately, one thought comes to me over and over: they're not finding the specific values in each line.
It is often said that art is about concrete specifics. Generality is the enemy of art. I think this is partly right, but also expresses the empiricist bias of our time. Art should integrate the concrete with the theme.
But I can see the point in this when I watch beginning actors. Their biggest mistake is to generalize; they think something like, "this character is angry in this scene," and then play every line angry without variations. That's bad acting.
The actor has to look for the possibilities in every line -- and this process takes more time than many actors like to spend. The actor should give himself a standing order to watch for passages in which everything he does is the same. That's a warning that he is not finding the specific values in the lines.
I like to act the way Hendrix played guitar: the odd surprise can come at any moment. The line can go anywhere. Sometimes grief can elicit laughter and joy can mean quiet solemnity.