I'm in the middle of reading Good Omens by Neil Gaiman and Terry Pratchett, and it occurred to me that I'd finally found a good place to ask a question I'd been wondering about for years. How do authors collaborate on works of fiction? Do they alternate chapters, or...? Is there any common, standard practice for this, or is it just whatever they want to do?
There seem to be two general approaches to this:
In either case, the collaborators will smooth out stylistic differences in a round of revisions.
Several years ago I wrote a short story with a friend. We talked briefly about the premise, then started writing. One of us would write a few hundred words and hand it over to the other. The other person would edit (focusing mostly on the language), then add a few hundred words and hand it over.
This process worked beautifully for us, for that short story. We submitted the story for our writer's group's annual "blind submission" meeting. Everybody thought our story was the best written of the dozen or so submissions. And nobody could identify who wrote it (we'd eliminated each other's "tells").
I doubt that this style of collaboration would work well for a longer story. For that, I'd probably alternate either scenes or chapters. Another possibility is to alternate POV characters. I'd also probably want a clearer shared understanding of the whole story arc.
I'm also working on several non-fiction books with a colleague. For those, we know the general scope of the books, but not the final organization. Currently we're in the "fleshing out the topic" phase. Each of us works similarly: Notice a topic that fits, that we have some passion about, and that we haven't written yet. Then write about that topic (usually as a separate file) and drop it in our shared repository.
Every now and then we get together and talk. One of us starts to ramble on a topic, and the other will take notes. That will spark the other to pick up some thread and run with it. Then together we shape the notes into something nearly coherent and add them to the repository to be fleshed out later (by whoever has the energy at the time).
This colleague and I have also written several articles together. We connect on Skype, open a shared Google doc, and start talking and typing. Sometimes one of us has an idea and writes a fumbling, inarticulate sentence or paragraph. Then the other magically figures out how to phrase it well. Often we'll each have something we want to say at the same time, and we'll simultaneously write in separate parts of the same document.
I much prefer a collaboration style in which we either write simultaneously or we trade off very, very frequently. The writing becomes a kind of improvisation (bounded somewhat by our ideas of what we're trying to create). As I said, I don't expect this style works for others, or for other kinds of works.