I've settled into a pattern of having two articles / chapters in rotation at any given point, and trying to complete one of them every month or two. I have a deadline of October 1 so I have one that's near completion for that, along with a chapter that I've been plugging away at. The idea is that the completed piece will drop out of rotation on Sep. 30 and I will add a new one.
My aim is to strike the perfect balance between focus and distraction. One is not enough because if I get stuck, then I waste time. Three is one too many, because I am not likely to make substantial progress on any one of the three.