I used to work at Amazon, and one of their internal "chatter" mailing lists had a tradition that every Friday people would write haiku, often about how their week went, or something in the news, or just something random. Going to try to resurrect that here.
If you want lines to color within, the "normal" requirements for a haiku are:
The essence of haiku is "cutting" (kiru). This is often represented by the juxtaposition of two images or ideas and a kireji ("cutting word") between them, a kind of verbal punctuation mark which signals the moment of separation and colours the manner in which the juxtaposed elements are related.
Traditional haiku often consist of 17 on (also known as morae though often loosely translated as "syllables"), in three phrases of 5, 7, and 5 on, respectively.
A kigo (seasonal reference), usually drawn from a saijiki, an extensive but defined list of such terms.
But of course often the 5-7-5 syllable structure is the only part used in Westernized haiku. Feel free to follow the guidelines above as narrowly or as loosely as you want.