Develop an idea for the musical. Before tackling the details, come up with the outline of a musical: a theme, a plot summary, memorable characters and genre of music.
Write the story line. The story should include an introduction where the audience learns about characters and their situation, development where the characters face conflict, followed by resolution where the conflict reaches a conclusion. Often, the introduction constitutes 25 percent of the play, development 50 percent and resolution is 25 percent.
Create characters. Focus on each character's physical appearance, his personality, mannerisms and speech, as well as his role in the play.
Break the story into individual scenes, set in a specific location and time and involving certain characters. Every scene of the musical should have a some significance in the plot, as well as a dramatic or comedic action or a song. End strongly with a song, surprise or shock, a joke or something that leads to the following scene.
Compose songs, beginning with a melody or lyrics. Songs in musicals often are reflective and reveal the thoughts of the singer or active and advance the plot, leading it forward. Songs must be a significant contribution of the play, not merely a distraction or something to kill time.
Write the lyrics. The lyrics must capture the essence and speech patterns of the character who sings it. Make the lyrics relevant to the plot, as well as the character's existence.
Compose the music. The music should complement the part of the play it accompanies: for instance, a love sick character may sing a slow ballad, while a character eager to embark on an adventure may break into a more uplifting tune. Also, make each song original and memorable, making it unique for the musical.