When your essay topic involves comparison, you can organize in either of two ways. First, you can discuss each thing separately and then include a section in which you draw comparisons and contrasts between them. With this organization, if you were comparing and contrasting two poems, you would write first about one -- covering, for example, theme, language, images, tone, and rhyme scheme -- and then about the other, covering the same areas. In a third section, you would make a series of statements comparing and contrasting major aspects of the poems. If you choose this method, make your separate discussions of the poems parallel -- that is, for the second poem, address points in the same order you used for the first poem. Also, in the third section of the paper, avoid simply repeating what you said in sections one and two.
A second way of organizing requires you to decide first which aspects of the poems you want to compare and contrast (theme, language, and imagery) and then to structure your essay according to these. For example, if you begin with theme, you state the themes of both poems and compare them. Then you compare the language of the two poems, then the imagery, then the tone, and so on. Two advantages of this type of organization are, first, you are forced to focus on similarities and dissimilarities and less likely to include material that isn't pertinent and, second, you avoid repetition by eliminating a separate compare-and-contrast section.
You can also combine these two types of organization. For example, you may want to discuss each poem's theme separately, and then move into a point-by-point comparison of the other aspects of the poem (language, imagery, tone, and so on).