Pick the subject. What do you want to write about? Any subject is fair game, concrete or abstract. Deciding on a subject first gives the project structure.
Draw a shape. The subject should inform the shape. However, it isn't necessary to choose something obvious. For example, shape a poem about the sun like the sun--or a Roman sun god. Creative design is as important with the shape as it is with the poem.
Write the poem. Don't shoehorn your poem into a shape. Write a poem that stands as good poetry on its own. Use the drawing as a guide, not a rule book. Impart meaning and imagery. Don't feel the need to rhyme at the expense of crafting beautiful poetry.
Combine the drawing and the poem. Each segment of your shape is a stanza. Using the example of a sun-shaped poem, the circle is one stanza, while the rays coming out are each their own stanza.
Edit your shape and poem. The shape and poem won't fit quite right when you first combine them. Take some time and make the two fit together the way you want.