Familiarize yourself with the poem, its author and the text. Even if you have read the poem a hundred times. Read it again, if you do not know all the ins and outs of the piece you won't be able to effectively argue your point, and the whole purpose is to persuade others to your side.
Create a strong thesis that you will argue throughout the essay. The thesis is one of the most important pieces of your essay because it sets up the rest of the essay and introduces the reader to your argument.
Include separate and distinct parts of the essay in this order: introduction, body paragraphs and conclusion. Use the introduction to draw the reader into the essay with an interesting fact or anecdote. Put the thesis towards the end of the introduction.
Use the body paragraphs to back up your argument with specific details from the poem, or other scholarly writings about the piece. Include direct quotes from the poem's text to further support your thesis.
Summarize your argument in the conclusion and how it relates to your thesis. You don't have to go over every single point of the argument, but you should reiterate why the reader should be persuaded to your side.