Wikipedia has a good article on the Haiku form- 5-7-5 gets taught in schools a lot but slavishly holding to a syllable count does not produce a haiku. The most important thing is the juxtaposition or twist which causes you to stop and think. Natalie Goldberg in Writing Down the Bones calls it "A Sensation of Space" - "If you read a lot of Haiku, you see there is a leap that happens, a moment where the poet makes a large jump and the reader's mind must catch up.". The Wikipedia article puts it this way "the subtle linkage or juxtaposition between the two sets of images within a haiku will be found to contain an interesting insight or spiritual message". Unfortunately it is rarely taught and leaves most Haiku wanting.
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Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho
