Review some common fairy tales or folk tales, and select one to use as your source material. For example, if you select "Cinderella," think of ways in which you can deconstruct or update the story, such as switching the roles and making the prince the one tormented by wicked stepsisters, and Cinderella the person who saves him.
Create your cast of characters. The principal boy should be good-natured, the heroine can be either really smart or really dim, depending on your story, and the dame is often the centerpiece because she is blustery, loud and boisterous. The villain should be obvious and broadly written, and fit the "mustache-twirling" bad-guy stereotype.
Choose the kind of music you want to write. Take popular songs and insert your own rhymes that make the song relevant to your story, or write your own lyrics. Above all, make the songs fun and humorous.
Structure the story into two halves. Begin by introducing the principal boy and the heroine and explain their daily lives. Use a song to help set the tone.
Introduce the dame and the villain, and explain the main problem that the lead characters must overcome in the story. Set the plot in motion with some dastardly act by the villain that requires a response by the principal boy and heroine.
Keep the plot moving with scenes of the boy and heroine trying to resolve the problem presented by the villain and failing several times. Write a scene in which all seems lost, but at the last moment, the heroine comes up with an idea that saves the day. End the first half with a song and dance routine as the heroes celebrate their victory.
Begin the second half with the principal boy and heroine seemingly happy after their victory. Write another song to express their contentment. Shift the action to the villain and describe his second plot.
Escalate the second crisis and show the principal boy and heroine dealing with this new problem. Write a scene that shows the heroes at their lowest possible moment. For example, the heroine is kidnapped and the boy is given a magic potion that makes him the villain's slave.
Provide a twist that changes everything. For example, the principal boy the audience thought was poisoned never drank the potion and is faking his stupor to get close to the kidnapped princess and rescue her.
Write a rousing climax that resolves the second crisis and shows the principal boy and heroine vanquishing the villain once and for all. Include a final song and comic routine with the dame, who summarizes the story and brings it to a close.