What about the content of the lines? How are they supposed to relate to each other?
Just let your creative juices flow and see what comes out. :-)
From Wikipedia:
Haiku is a very short poetic form. Traditional Japanese haiku consisted of three lines of 5, 7, and 5 units each, which are generally applied as syllables, and contained a special word—the kigo—that indicated the season in which the haiku was set. Some consider that a haiku must also combine two different images, be written in present tense, have a focus on description and have a pause (the kireji or "cutting word") at the end of either the first or second line. All such rules are somewhat arbitrary and are habitually broken by most poets, especially when adapted for languages other than Japanese.</blockquote