My colleague Kasey Mohammad is contributing a series of National Poetry Month blog posts at the National Poetry Foundation Harriet blog. The most recent pair of posts–here and here highlight Roman Jakobson’s theory of the functions and orientations of language.
You can check out his series on Poet’s Ear here and here and here and here… or should it be hear, with the verb enveloping the auditory organ.
If you want more poetic theory, you can check out the summer INWA workshops here.
Or work through the eight volumes of Jakboson’s Selected Writings.