To me, one of the best things a writer can do is read and study poetry. We often forget the different things we can achieve through writing, and by looking at poetry, where different techniques are more obvious, we can find so many more tools to use. For example, poetry is a great thing to look at for pacing. If we look at the way poems speed or slow our reading, we can try to put that in our own writing. If we read a poem that uses long lines, but you get a random staccato two-word sentence, it stops us and draws our attention. We can do that in prose too. Beyond pacing, poetry can really help with imagery, metaphor, and attention to details. Since every word matters, we can also better see how our word choice effects the reader in poetry. Some great poets for pacing are: Allen Ginsberg, Olga Broumas and Jorie Graham. Some poets who have terrific imagery are: Brigit Pegeen Kelly and Sharon Olds. To see great examples of voice, check out: Frank O'Hara, Ai, Amber Tamblyn (yes, she's a terrific poet too), and Kenneth Koch.
Great tip, Ryan! I did a study on voice during my last term at school and my professor had me pick up a book of poetry called Asphalt Georgics by Hayden Carruth. It was really interesting to see how voice can be established in so few words.