A “ghost line” (per Rachel McKibbens) is a line you use to prompt or inform a poem, but erase from your work at the end. You can use a ghost line of your own devising, from daily life, or borrow one from another artist.
Try starting your poem with a ghost line: delete it when your poem has taken shape. Here’s a possible example from Jason Carney’s Starve the Vulture:
Faith without works is dead.
Boston Poetry Slam Online