Writing as we are about literature, there are certain elements that must be in every esssay. First, you want to name the author and the title of the work. Second, the particular themes you want to focus on, and third, the structural elements--irony, imagery, diction, tone, prosody, etc.--that express those themes. In other words, you have to have a point to make about HOW the poem expresses its WHAT, that is, its subject. Which, by the way, is usually something found beyond the first reading.
So: we can mix this up a little, but the formula should be something like this:
Billy Collins' poem "Whatever" is a delicately phrased sonnet that uses tactile images of decaying leaves and barren fields to evoke the futilty of a selfish love.