The form of a poem dictates how it appears on the page and how the poet deals with his or her material.As with all writing tasks, the poet needs to begin by asking "What kind of poem am I writing? What is my audience? What is my purpose?"Some of the purpose answers might be:
to tell a story to describe a scene
to express an emotion
to make a comment on life
to tell a joke
to advance an argument
The next question might be: "What kind of poem shall I write?" Some answers to this question might be
a haiku free verse
The poet's choice of form might be influenced by the audience being aimed at, but it is more likely to be determined by the nature of the material. For instance, a rap is a good way of expressing emotion and telling a story, but it might not go down well with old age pensioners.
Different forms have different strengths and weaknesses. For example:
Haikus are good for describing and expressing emotions but not much use for telling stories.
Limericks are good ways of telling jokes but not ideally suited for expressing deep emotions.
Ballads are good for telling stories but aren't used often to express arguments.
Sonnets are a very good way of reflecting on a scene or an idea but are not well suited to story telling.