Tension is one of the biggest--if not the biggest--factor that determines the strength of a poem. A poem without tension will read as dull and predictable. Even though poems are short, you want your reader to hang on to every word until the poem is finished.
One way to add more tension is through line breaks. A good line break leaves the reader wondering what comes next. Here's an example of a stanza with a decent line break from my poem when mermaids sing.
Example: "a warm purple glow
two lily petals
part the glimmering
darkness"
The line break at "part the glimmering/darkness" adds a little more tension to the poem because of the way it broke off the line. I could've said "part the glimmering darkness," but having "darkness" on that line takes away from the tension. Instead, by moving it to its own line, the break forces the reader to take a quick moment to pause, which leaves room for them to ask themselves "what are the lily petals parting?" This will have the reader briefly guessing what comes next, which keeps them engaged in the poem.
