OOC - How Do You Create a Joint Post?

So, I was about to try to explain to someone how to make a joint post when I realized that I've never actually successfully written one before. The one time I tried, the post became a cluster**** when it turned into a p****** contest between myself and one of the other writers of the post. In retrospect, it would have been a good idea for us to have agreed upon what we wanted the end result of the post to have been before we got super-far into it, and if we ever do try to pick up the pieces, I will recommend that.

That said, I suspect I would still be the blind leading the blind if I tried to explain the nuances of a joint post to anybody, however, a lot of you guys have quite a bit more experience than I in this regard. So far, all I have is:
1. Google Documents is your friend, and
2. Have an agreed upon course before you write.

What other advise do you platformers have for how to write a joint post?