From a writer’s point of view, the essential elements are the same. The difference is the delivery of the story. In fiction the story is presented by a narrator, either omniscient, or all knowing, or by a first person narrator, whose point of view is restricted to their experience or observations. Although rare, there are examples of second person narrators, which are combinations of the hero’s experience and an all knowing omniscience. The playwright must deliver the entire story through dialogue, without the benefit of a narrator. A novelist may send his hero all over the world and have him engage in spectacular scenes of action, where the playwright has only a bare stage to present the story, where car crashes and gun fights are both difficult to stage and nearly impossible to believe. Therefore, the playwright is more focused on the emotional experience of the hero, and the universal experience of the audience, while the novelist may include that as a focus, while also portraying the hero as an active participant in natural (or unnatural) settings, affected by events either within his control or beyond his control. Both the novelist and the playwright must enable the suspension of disbelief, but the playwright may have a more difficult job of it.
The first and most important difference between these two poetics (in Aristotle’ view) is the way the piece is narrated. Fiction is “imitation of an action by language with more than one narrator” and drama is “imitation of an action by language without narrator.” Thus, from a writer’s point of view, the choice must be made whether the characters speak in their own voices in “dialogue,” or whether a narrator (omniscient or otherwise) assists the imitation with descriptions, psychological analysis, philosophical comments, and the like. In dialogue, the characters speak “speech acts” – statements, questions, requests, announcements and the like – and only their onstage actions (arriving, leaving, fighting, etc.) can assist their speech-acts. A group of designers – stage, costume, lighting, sound – add their own “languages” to the imitation. In fiction, these details are added by a narrator (“It was a dark and stormy night”). Of course, in practice the lines are often blurred (for example, Tom Wingfield in Tennessee Williams’ Glass Menagerie serves as a kind of narrator).