Whether you're teaching to a classroom full of third graders, or you are an aspiring poet fresh out of college, shape poems are a type of art that help you to develop your style and express your ideas. For younger learners and beginning poets, have them create a simple shape with their words. For example, you could ask them to follow the style of Dorthi Charles' Concrete Cat. Take them on a walk outside and have them be inspired from some source of nature.
Another important aspect of writing a shape poem is to avoid forcing the image. Write down some words and play with them. Remember, it might take awhile before those words can truly come to life in a shape. Don't feel constricted by others' perceptions of reality. For example, if you were writing about a box, you could add vertical lines throughout the length of the box to represent a prison and how "thinking inside the box" essentially keeps a person's mind trapped.