It's interesting to me to consider the ways in which poems make reference to other poems. If we read whatever poetry we read, looking for these relationships, the frequency of their appearance is notable. From casual literary allusion, to allegory of biblical proportion; from subtle melodic shifts that echo familiar songs, to the appearance of Osiris or some other archetype at your screen door on a sunny morning while you're trying to read something postmodern...poetry seeps like a smoke through the mesh.
It is difficult to imagine a poem that stands on its own, with no support - or influence - from some other poetry. The support might come from as near as within the poet's own work, or as far as a time on the other end of history, in a town on the other end of the world. Each new poem is permeated by the history of poetry, and the poets wander cartoon construction sites, dropping from beam to beam of the shifting forms and architectures, with their own surprise their only punctuation.
The poet might write a poem that references his own work in any number of ways. Select a poem that you've written, and write another poem about that poem. The new poem might be a recounting of the experience of writing the initial poem, or it might be an analysis of the initial poem from a previously unconsidered perspective. It might be a set of additional notes, afterthoughts, or an alternate history (reimagining the poem as written by someone other than the poet, for example).