I. The structure remains similar. Three lines. It's mandatory.
II. There are no less than 5-7-5 syllables, which is based on the haiku model. It's also mandatory.
III. The rhythm is meter. Since we don't speak in syllables, I contemplate the meter of each line. Thus there is no set number of syllables, although I consider the flow of our language. I am not bound to it, but I am aware of it. Consider the following poem from my upcoming book:
Beauty and beholder
Eye of newt and bestial lover
Early grave dug shallow
Has the following rhythm (a '\' represents the stressed syllable):
\ u \ u \ u
\ u \ u \ u \ u
\ u \ u \ u
A lot of the time the rhythm of the first and third lines begin stressed, whereas the second line begins unstressed, or vice-versa.
IV. Line two must always be at least one syllable longer than the first and third lines. Natural language would dictate at least two syllables (or more pairs), but it is not mandatory. An idea/emotion/observation still has to be fully conveyed. If you were to gauge every poem in my book, you would find the meters/counts are all over the place. It may be 5-7-5, 5-8-6, 6-10-6, etc.
As you begin to read my poems, in chronological order, you will see I stick to the 5-7-5 model, due to my desire to attempt to write traditional haiku. Once I shed the idea that unless I were writing in Japanese, I really couldn't write haiku properly, did I begin to develop my concept further.
V. Subject matter must deal with us humans. Not nature, as the Japanese have been doing for centuries. It could be an emotion, or an emotional state. It could be about some experience. It could be about some observation, of yourself, another person, or a society. It could be about an abstract, such as death, or evil, or good. This too is mandatory.
VI. Be creative! There are so very many ways to manipulate the English language, it's a hoot! We have homonyms, synonyms, repetition, hyperbole, etc. - all that fun stuff you may have studied in high school or college. Now is the time to utilize it! Given the confines I've outlined above, though, you've got very little room to maneuver, so you better know what you are doing!
That's it! Follow these few simple rules, and you too can successfully write Psaiku. Go ahead - try it - experiment. Then share your work, for without sharing, we cannot further this new form of poetry. Forget sonnets or haiku - let's embrace an intense new literary art for an intense new millennium!