Use a word processor that makes columns. Type the title of the poem at the top of the page, drop down two double spaces, and use the "Page Layout" menu to create two columns. If you'd rather write by hand, use a ruler to divide a sheet of paper into two columns.
Write your poem. Think about the way the poem will be delivered. The poem, like any, should have a theme. Your theme, or the subject of your poem, can be anything you like. The idea is to keep the theme consistent for both columns. Though the poem is written to be performed by two readers, it should be considered a single poem that stands alone.
Incorporate two voices or readers by using creative devices like writing a call and answer poem. The left column text could be a question or statement (a call) that requires a response (answer). The right column will contain that response. You could also consider a contrast poem whereby the left or right column delivers a positive message the the other column delivers a negative one.
Use traditional poetic devices such as metaphor and simile. Pay attention to the meter and rhyme scheme as you write, distributing them evenly between the two columns. Read the poem with someone else to ensure it flows. If you don't have a partner available, record yourself reading one column and read the other column on the playback. The two-column, or two-voice, poem should read as a unified poem, but it is primarily a performance piece and should be considered as such.