Choose an instrument. Many music composers use a piano to write a piece of music. Select an instrument that you feel comfortable playing. You should not struggle to play an instrument while writing the music. (reference 1)
Decide the type of musical piece you want to create. There are numerous ways to play a song and you should think about how you want things to sound before writing. (reference 1) For instance, ask yourself what mood you want to convey. Think about the song's tempo, key, and the notes you want to use in it. Determine if you want to use smooth rhythms or jagged sharp rhythms.
While utilizing your instrument, brainstorm musical ideas. Begin by playing random notes or chords. It's best to experiment before writing anything just to get a feel for what you like. Develop different ideas that are pleasant to your ear. (reference 1)
Pick one musical idea and develop it. Think about how you could improve its sound. Stop playing for a moment and think about how the piece should sound in your head. (reference 1) Sometimes humming the piece can help determine how to play it. (reference 1) Continue playing the piece and refine it until you are happy with the outcome.