Realize there is no definite structure when developing a musical.
Decide if your musical is a collaboration effort. There are three roles in the creative collaboration of developing a musical: lyricist, librettist and composer. The lyricist writes the words for the songs, the librettist or book writer creates the dialogue and the composer writes the music. These roles are often combined.
Understand that collaborators often work in different ways. When the roles of composer and lyricist are combined, sometimes the lyrics and music are created simultaneously. When this is not the case, the lyricist and composer teams work together. There is no answer to the question "What comes first, the music or the lyrics?" Instead, find out what works for you and your team and go from there.
Look online for tutorials about writing music if you get stuck or realize you are having difficulty. Several websites are listed in the song writing section at the Kenlyen website.
Learn about writing plays. A musical, by definition, is a play in which music is an essential element to the dramatic structure. Books such as "The Playwright's Guidebook" by Stuart Spencer and "The Playwright's Process: Learning the Craft from Today's Leading Dramatists" by Buzz McLaughlin are good places to start.
Decide what structure you want to use to frame your play. The most frequently used structure is the Three Act Structure, also called the Aristotelian Structure. This structure is comprised of three parts called the Prostates (exposition), Epitasis (complication) and Catastrophe (resolution).
Write your play to be read. While musicals are meant to be performed, they must first survive several readings by a variety of people before they are passed along to the person in charge of putting the musical on the stage.
Follow the manuscript format when submitting your musical to theaters, playhouses, publishers, contests and the like. Be sure to include a title page, cast page, musical number page, act or scene headings, at rise descriptions, character names, dialogue, stage directions and transitions.
Use an easy-to-read font at size 12.