If you want to write a song, always start with a Big Idea, that is, something you want to write about.
Translate your Big Idea into a Strong Title, which summarises the Idea.
Imagine what your song might sound like, if it were played on the Radio, which may suggest a style or genre you want to develop.
Outline a plot, with beginning , middle and end.
Sketch out the lines of each part, initially in prose, You can edit these later.
Find a strong opening line, to capture the audiences attention.
You may prefer to start with the chorus, from which the composition of the verses may lead into and follow from. Use your Title to start the chorus and listen for a strong melodic Hook.
Perhaps include a pre-chorus, which serve to lead into the main Hook line.
Keep in mind the song form, like Verse/ chorus or 3 straight verses.
Keep the listener's interest by adding some musical variation with a Middle section, which may make some observation about Life in there context of the song.
rewite, rewrite, rewrite add rhyme and rhyming scheme like AABB and a meter like
i BET you’re SAG -i-TAR-i-us
taTUM taTUM taTUM tata
Sing your words to an interesting Melody. If you plan to sing your own song, take care to find your natural pitch.
Find the root notes in the melody line and formulate the chords which harmonise with the Melody.
Decide which Rhythm and Tempo best serve the lyrics and the Big Idea.
Rewrite and rewrite until the song is right.