First let me explain what Narrative improv is. As you can tell Narrative tells a story from beginning to end, where as most forms of long form use callbacks to connect scenes, a Narrative follows one story from beginning to end. The story usually follows a protagonist who has an overarching want that drives the story of the musical, an antagonist who tries to get in their way, and the protagonist either getting what they want in the end, or they realize what they've wanted all along is not what they wanted and they're happier knowing what they know now. This may seem impossible to accomplish, but it's fairly easy if you break it down scene by scene.
Scene 1: Protagonist Want Scene
This is the scene where we meet our hero! The scene should be driven by their want, if there's no want in this scene then your whole musical will be lacking a strong through line. Your hero's want could be anything, from wanting to be the queen of the world, to going to the big dance at the barn. As long as their want drives their character motivations.
Scene 2: Antagonist Philosophy Scene
A lot of musical improv groups assume that their antagonist scene has to be the opposite of the want song. The antagonist should have a philosophy that helps drive their story line, they are meant to have their philosophy get in the way of the protagonist's wants. So if the protagonist wants to go to the barn dance, the antagonist shouldn't want to stop them specifically from going to the dance, they should keep in the same theme and want to have all the barns in town replaced by malls. It still prevents the protagonist from getting what they want, but is more surprising than just wanting to stop someone from going to a dance.
Scene 3: Charm Scene
In most musicals we always have a scene that while entertaining, doesn't really have anything to do with what is happening, and is used to break up the action. This can be seen with "Shapoopi" from The Music Man, "Coffee Break" from How To Succeed in Business Without Really Trying, or "Bend and Snap" from Legally Blonde. Peripheral characters usually sing these and they can drive the plot, but they don't have to. In musical improv this can be a chance for the people who aren't main characters to just get out and do a song that is silly and ridiculous that gives the other characters a chance to think about their next move.
Scene 4: Moment of Doubt
In all musicals, we see our protagonist have a moment of doubt. This is the moment where they rethink all of their motivations, and ask themselves whether their want is really what they want. It is usually caused by a stumbling block that the antagonist sets up in their path; for example, let's use our "Barn Dance" want. In this scene our hero would see a sign on the barn that it's being readied for demolition or a sign that reads "Future Home of Pine Cove Mall." This catalyst would propel the main character to sing a change song, where they doubt themselves and their motivation.
Scene 5: Resolution
This is the scene where the protagonist either gets what they want, or realizes that they made a mistake and are happy just the way they are. It is also a chance for your antagonist to either have a change of heart, or stay the same. The Charm Scene characters can sometimes come into this scene and help to wrap everything up, but it's not always necessary. This scene should end with a big group number.
So there you have it, a breakdown of narrative structure, so come to The Player's Theater, the last Saturday of every month at 10pm to see it in action. *plug plug*