Writing an essay about the meaning of a poem involves several levels of reading in order to find the various types of meaning the author conveys.
The first approach you can take is trying to understand the author's intention. For this, you need to determine the genre of the poem. Is the poem serious or humorous? Is the author suggesting something seriously or composing a parody? Next, research the author'sw biography and historical period to understand the context in which to read the poem.
Once you start looking at the poem itself, you first need to understand the literal level. That involves looking up unfamiliar words or words used in an unusual manner. Next, pay attention to the syntax -- make sure you know the antecedents of pronouns, which nouns go with with verbs, etc. Note any allusions or intertextualities. Then do a literal prose paraphrase.
Finally, look for allegory or hidden meanings./ Is there a possibilty that the author has a second non-literal meaning?