There are a great many poetic forms, both rhyming and not, but a lot of these are more classical in nature. People still use them regularly, but poetry of our day has a much greater focus on alliteration and assonance for its rhyme, and often eschews meter in the strictest sense. An intrinsic understanding of form is important for a poet, as it's the understanding of form that better helps one to let go of it in ways that still hold things together. Even with most forms, however, I don't think your average poet "plans" anything other than the basic building blocks of that chosen from, or a basic idea, or even just a simple starting point. One of poetry's strongest advantages versus prose is how easily and quickly it can evolve.
