Free verse seems to be the most popular style here (you just write basically).
But if you want to be like the GREATS I suggest you look up rhyme scheme (could be AABB, or ABAB, or AABC, etc) and meter (the length of a line measured in syllables).
(mouth waters) And throw in some poetic devices (metaphor, simile, personification, alliteration, onomatopoeia,etc...).
Think of the message you want send out before hand.
There are rules to poetry too, don't be fooled.
But of course you can always break away from the rules and write up what's in your mind!
I'm out
