Teach the various types of figurative language, including irony, synecdoche, metonymy and metaphor. Irony means writing or saying the opposite of what you mean. Synecdoche means using a part of something to refer to the whole of it. Metonymy means referring to something indirectly or by another name. Metaphor means the comparison of two things that are not obviously similar.
Show your students how different poets have used the same images in various contexts to express different meanings. For example, Virgil in Book VI of "Aeneid" compares the bodies of the dead in Hades to "the leaves in the woods [that] fall down with autumn's first frost." Dante borrows this simile to describe the suffering souls in hell, but Milton recycles it and charges it with new meaning by applying it to the gigantic bodies of the fallen angels in Book I of "Paradise Lost."
Show your students that its difficulty is what makes poetry interesting. According to literary critic Northrop Frye, poetic figurative language "doodles and riddles us" -- that is, it charms us and, often deliberately, puzzles us, and this is precisely why it is worthy of our attention.