Do the same for differences. Organization is tricky. DO NOT isolate the two poems in your discussion. You might consider comparing and contrasting the poems side by side all the way through. This organizational strategy allows you to organize your paper into discussions of theme, metaphor, etc.
Textual support is essential to a good essay, no matter which approach.
The same caution and care should be taken when quoting poetry as when quoting books, journals, periodicals, etc. A poet is the author of his or her work and should be quoted word for word. However, unlike prose, poetry uses form, punctuation and other devices to express a theme or subject. Therefore, careful quotation is imperative to your understanding of the poem. Check out How to Quote Poetry for more information.