Select the theme of the poem. This is entirely up to the poet and no theme is inappropriate for art. Read about some common themes at LitScape.com. Themes include love, nature, death, motherhood, loss, among an infinite list of others. Find other poems at the Academy of American Poets. These poems are written by established poets who have mastered the art of many styles, including the theme poem.
Select the kind of form in which the poem will be written. While historically the poem has rhymed and taken a specific shape or meter, modern poetry has seen a change in style and sound. Determine if the poem will rhyme, be written with free-verse or have be in haiku style. Read Writing.com to discover the many styles, rules and patterns, then decide which will be appropriate.
Think of a tone or aesthetic and write down a list of words that may be fitting. While some poets brainstorm before writing a poem, others simply write spontaneously, editing later. Writing down a list of words can be helpful when starting a new poem. Focus on an idea or feeling. Select specific words--poetry can be happy, somber, bright, eerie or anything else the writer would like.
Write the poem. Use the interesting words listed and keep to the theme. If the theme is nature, for example, make sure to use imagery that evokes the idea. These could be colors that are common during seasons, words that describe temperature, descriptions of the outdoors and how people feel at different times of the year.
Read the poem for clarity and make sure it fits the style in which the poem is written. Editing poetry can be hard, as most writers feel overwhelmed at the thought of changing their own work. Erase cliches, make sure every word is useful to the poem and read it aloud to make sure it flows correctly.