Let’s get back to basics (no pun intended). In this exercise, you’ll write a new song from scratch, limiting yourself to only two elements.
Forget a full band arrangement. Heck, forget chords. Write a song consisting of only a melody and a bass line. [For you bassists, resist playing chords or double stops. That would defeat the purpose of the exercise.]
So focus on these two musical elements: melody and a bass line. A chord consists of at least three notes, so technically, your song won’t have any chords. Even so, a listener’s ear might ‘fill in’ chords, that is, might feel a chord is implied at any point in the song.
In the process of focusing on these two elements, you might learn just how important a bass line is. You bass players can thank me later.