Common measure, also called common metre or ballad metre, is a form that follows a simple metrical pattern and rhyme scheme. However, the form, in its simplicity, lends itself to a gentle sway that is quite musical to the ear, and can be used to great effect in telling a story poetically.
To explain it simply, common measure is written in an alternating pattern of iambic tetrameter and trimeter, with a rhyme scheme of abab, although in ballad form, which is a variant, the trimeter lines are not required to rhyme, and may have a rhyme scheme of abcb. If unsure about meter, please reference the following link:
This poetic form is an exercise in understanding the musicality of poetry. What I mean by this is that, when done properly, the iambic metrical pattern, combined with the alternating lengths of the lines, gives a feeling of being on a boat in a gentle breeze, where the waves lapping the hull beneath rock the boat.
When writing common measure (and, indeed, any form poetry), it is important to understand that it is as much for the ears as it is for the mind. This means that poetry is meant to be recited aloud. The flow of the lines, and the entire piece, are brought to life when one is allowed to really hear the words. Those natural stresses carry a forcefulness with them, bringing a subtle but very real power to the piece. As such, take the time to read your stanzas out loud to yourself, or to someone, much as one might when composing a piece of music, because it helps to play the music so the ear can hear. Feel the ups and downs, adjust as necessary. A trochee or a spondee are sometimes very necessary, but again, reading your lines out loud is paramount to achieving your aim.
With this said, I will leave you with a common measure poem of my own, Songs of the Eventide.
Thanks for stopping by, and to steal a line from the late great Bob Ross, happy writing!