Recently, I was giving feedback to a young writer friend who was working on his first play. His first draft showed that he was struggling a bit with play structure, so one of the ideas I introduced to help him was "the question of the play."
The question of the play is, quite simply, the question that the audience is waiting to have answered so that they can go home. In Romeo and Juliet, the question might be "Will they stay together?" In Hamlet, it's "Will he get revenge?" It's actually a sneaky way of giving your play structure, as every scene in some way needs to lead us closer to answering that question. What's the question of your play?