a. Plays are not conversation, nor are they discourse(Discussions of an idea).
b. Plays are stories told in action. Everything Aristotle wrote about play writing (which he called Tragedy making) indicates that.
c. Plays are stories about someone's emotional reaction to a situation and what that reaction causes him or her to do.
d. A playwright fashions a play, he does not write it. He expresses the fashioning of the play by writing down what he has created in terms of stage directions and dialogue..
e. Thus the fashioning of the story is what the playwright does first. He tells the story in theatrical terms, which means he creates an situation and places a person into it. That person has an emotional reaction to the situation and does something that expresses the reaction. (either the situation or the character's response to it is a disorder that must be repaired) A chain reaction of his action causing an emotional response that causes an action that causes an emotional response......and so on until the story is complete by order being restored. The playwright creates no dialogue until he can tell the story in terms of action/reaction with no dialogue at all.
As an actor, you need to be an emotional responder to the stimuli of the play moment by moment. Those responses will also contain the action of the play (what you need to do as an actor).