Choose a subject for your portrait poem. This should be someone you know well, or at least know a lot about. You can write a poem about a family member, friend, significant other or love interest. Alternately, you can write a portrait poem about a famous person or other public figure.
Make a list of your subject's qualities. While making this list, you should include different types of qualities, including both physical and superficially noticeable features, as well as more personal traits (such as beliefs, attitudes and concerns). Also, if you're writing about someone in your life, consider listing memories and shared experiences you have with this person.
Write a draft of the poem, incorporating words and phrases from your list. Portrait poems do not have to rhyme, but including some sense of rhythm can be helpful. For example, one may use a recurring word to start several lines within a stanza, as in this short poem:
My father
Born in Tennessee
Is a wise man
Who learned of hard work
Who raised three children
Who taught them respect and honesty
And went without to give them more.
Revise and edit the poem until you feel it is complete. Substitute words that feel overused, seeking similar words from a thesaurus. Remove phrases that feel clichéd, and add detail until you feel the poem accurately depicts your feelings. Read it aloud to assure it "sounds right" to you.