Choosing a Form

[Wildcard]

   Since becoming interested in poetry I have been drawn to learning about different forms. In some of the books I've read, they suggest that some forms are better suited for one type of poem. For example, Haiku has rules about content and therefore excludes some topics, but free verse is unrestricted and can be about anything.

My question is this: How do you decide what form you will write a poem in?