There are as yet no fixed rules about how to write haibun, and very possibly—one might say, hopefully—there never will be. The following ideas are not rules, but merely tips that I have learnt from hard experience to be helpful when writing haibun.
There is general agreement about what haibun is attempting: a marriage between prose and haiku in which the two are equal partners. As in good marriages, the partners grow through their intimacy; by combining their individual talents they are stronger as a duality than either partner would be on his or her own. Success depends a lot on both partners accommodating each other, adjusting their behaviour so that they get on. Yet partners also need to retain a measure of independence and their proper integrity, to have the chance from time to time to express themselves and 'blossom in their own way.'
Which do we start with, the haiku or the prose? Personally speaking, I find the best haibun tend to use pre-existing haiku, very likely haiku that have already appeared in print without any consideration of them later forming part of a haibun. A haiku may even record an experience or observation at an entirely different time and place from the occasion chosen later to be the subject of a haibun; but somehow it fits in well, even if it may need adjusting. It may even not matter if the haiku takes us right out of prose context; the connection may seem mysterious, but if it is faithful to the poet's intuition, and not artificial, there is a chance it will engage the reader too.
Occasionally the opposite happens: whilst reliving a personal experience and recreating it in prose, I discover some fresh aspect of the situation, one that stirs up enough feeling to release a new haiku. Whatever else, any haiku in a haibun should, I believe, be strongly evocative, full of feeling—not serve as a chorus to the prose narrative.
It seems to me necessary to insert the haiku judiciously, not simply because 'it seems to be about time we had another one.' I know writers who seem to work to a formula—one haiku at the start, another at the end, one every 50-100 words in between. This is a sad case of form taking charge of matter. If there are too many haiku they seem to interrupt the flow, in a way that is irritating to both the reader's eye and his/her mind. I try to find just those few places where the prose shifts in a new direction, either a change of mood, or where time passes and a new situation arises. This is not unlike the 'link and shift' principle employed in renga.
When you think your haibun is 'finished,' try reading it aloud to yourself. If a haiku is indistinguishable from the prose and therefore inconspicuous, something surely needs to be done. There are three choices: it can be strengthened, it may sink back into the prose, or it may disappear.
Is there such a thing as a prose style specially suited to haibun? It has often been suggested that, as a principle, 'haibun prose' ought to have features similar to those we admire in haiku: concision, directness, plainness, everyday vocabulary. This seems to me to be a recipe for utter dullness and will obviously make it harder to distinguish haiku and prose when the haibun is read aloud.
My recommendation would be to consider the use of different prose styles to suit different purposes; to suit the atmosphere of the chosen scene and the mood of any characters involved in it, to reflect the 'pace' of happenings. In a very long haibun, in which a series of distinct episodes are related, it may well be appropriate to ring the changes between different styles suited to different events or situations, and this variety will give interest and vigour to the whole. Plain, incomplete sentences may work well if you want to create a scene with an economy of words, e.g. Came to the market place. Saw a stall selling fruit. Strawberries ripe enough to make a mouth water. But not enough pennies in my pocket to buy any. That sounds like someone in a hurry and eager to get on to another point, perhaps talking to him- or herself, something we call 'stream of consciousness.' On a different occasion you might indulge yourself in a more literary 'purple passage,' perhaps using expansive sentences of six, seven, even eight descriptive clauses—frankly, to weave a spell over your the reader, whom above all you must entertain.
Don't overlook the liveliness and impression of character that use of direct speech will create. Haiku are an opportunity to briefly introduce other creatures who are not principals in the story, thus creating a greater ambience.
Haibun may be written successfully in first, second or third person. It matters which one of these you choose. Perhaps you begin by writing a personal anecdote in first person. Try converting it into third person. You may be surprised how much more effective or how much less self-concerned it sounds. This tactic may increase the general relevance of the piece.
Transforming your own experience into a third person account may also free you more easily from 'being completely honest.' Haibun is a form of literature, not of confession. You don't have to write 'the truth, the whole truth, and nothing but the truth.' Alter the facts if that improves the story; all you owe readers is the illusion of truth because they weren't there to see what really happened. There are several ways the truth can be 'improved': by changing the order of events (something Bashō constantly did in his haibun); by embellishing the truth (Bashō did this too, for example in his famous haiku about seeing the Milky Way leading across to Sado Island—research has shown that he could not have seen this phenomenon at the time and place where he was standing); and by cutting out distracting details.
I never get a haibun right first time. It always takes me several drafts, and even then I may have to abandon the project as a failure. The tendency as draft succeeds draft is not for them to get longer, but shorter, for I recognise distracting details that play no essential part in the haibun. To be a good haibun writer you need to be a good editor. For the one essential rule about haibun (as with haiku) is that it should be interesting and not wearisome. To be interesting it almost certainly needs to contain something unusual or surprising, and build quickly towards a climax and a resolution/ denouement.
The general reading public are likely to judge haibun by comparing them with short stories with which they are more familiar. To win their interest and approval, the haibun writer has to aim at something even more effective and more interesting, not less.
First published, in a German translation by Claudia Brefeld, in Sommergras No. 90 (September 2010), under the title 'Einige persönliche Gedanken über das Haibun-Schreiben.'