Going on the assumption that you have the four poems that are to be compared, you will probably want to write a comparison/contrast essay about them. (See the link below for help with the essay writing.) In drawing comparisons and contrasts, you may wish to examine different aspects of the poems. In order to make an accurate examination of the poems, you will need to "break the code" of each poem; the success of doing this lies in understanding the literal meaning and the figurative meaning of the poems. What is literal and what is not can shift, depending upon the context of the poem. To understand the interweaving of the differing contexts is to take the greatest step in analyzing poetry.
Moreover, the most important thing to remember and to recognize is poetic metaphor for metaphor sits at the center of poetic expression. Poetic metaphor is a frame of mind, a way of looking out from an inner world of essentially personal thoughts and feelings. In the act of expressing these thoughts and feelings, the poet shares them with the reader or listener. So, identify the controlling metaphor of each poem. After you identify the controlling metaphor(s), meaning emerges from the poem(s).
Here are some other points to consider:
1. Theme. While all the poems you compare may have similar themes, there may be differences in meaning or expression of this theme.
2. Form Are the poems in any kind of traditional form such as ballad, sonnet, etc? Are they similar or different? How do these forms affect the meaning of the poem?
3. Language and Literary Devices What metaphors, similes, imagery, alliteration, connotations, irony, etc. are in the poem? How do these devices further the meaning of the poem?
4. Rhythm and Rhyme Is there a rhyme scheme, what meter is present? Is there internal rhyme as well as external? Do these rhymes, etc. influence the meaning of the poem?
Before you begin the essay, then, you will want to list all the elements of each poem and how they contribute to the poem's meaning. Then compare and contrast the poems to each other. As an example, there is a link that provides you an analysis of a poem. Good luck!