I co-wrote a novel, The Swiss Courier (Revell 2009) with Mike Yorkey. Mike wrote up his post about how we worked, and then he sent it to me. I then took the post, tweaked it, and I added my flavor and thoughts ... which is pretty much how we worked on the novel!
Mike and Tricia started by working hard on the one-sentence and one-paragraph synopsis for "The Swiss Courier," and then they began fleshing out the characters. They also firmed up a basic plot. They next wrote a couple of chapters, with some back-and-forth, and then it was off to the races for Mike. He was the lead researcher and writer. He knew where to take the plot. To use Mike’s horse-racing metaphor (Tricia knows nothing about horse racing!), Mike was the one doing the running in the co-authoring relationship (doing the writing of the rough draft), and Tricia was the jockey, making sure Mike was going in the right direction. This meant Tricia edited—told Mike what worked, what didn’t work, and why. Tricia also cut out chunks and added chucks, but she doesn’t know how that ties into horse racing! Mike won't say Tricia beat him with the whip, but she reined him in on some areas and then gave me a "hand" ride (a horse racing term for slight guidance) so as not to stifle his creativity. All the way, Mike and Tricia both knew where the finish line was, and they think it was a winning horse-and-rider combination.
From Mike, with Tricia’s additions and revisions included