Make a list of challenging words and terms in the poem. For instance, in the Charles Wright poem, "In the Valley of the Magra" from his collection "Appalachia" (1998) define Magra. Indicate to readers that it is an Italian valley region between Lugiana and Tuscany. This informs readers with a way to contextualize the poem. Continue finding and defining words and terms throughout the piece.
Compile the list of terms, phrases and your definitions. Think up a way to display the information. For a long and historically rich poem, like T.S. Eliot's "The Waste Land" (1922), consider using a footnote key.
Insert a small footnote number by each line. Add a corresponding number at the foot of the page which provides a definition or context for that line in the poem. If you only need to create a limited key, include it on a separate page or in the back of a collection of poems. Mark a letter or number by the line in the poem. Insert a corresponding letter or number in the back of the poem that enlightens the reader with information or personal insight.
Condense the key. Choose the clearest, simplest words possible in key. A reader does not want to have to use a key for your key. Write clearly. Ask a writer and a reader to edit your work for clarity.
Consider alternative key-making methods. For instance, use images in the key. In the above mentioned Charles Wright poem, for instance, include a photograph of the Magra Valley instead of a worded term. As an experimental approach to a poem key, ask for feedback from readers about their experience of using pictures to read through a poem.