You must set hard deadlines for the completion of papers.
I think at first this statement can seem either obvious or irrelevant to many people, but I'll explain why it is certainly not irrelevant.
First of all, it doesn't matter how good your work is if you don't communicate that work to the outside world efficiently. You won't be able to continue your good work because you won't be supported. And if you are in a collaboration your work depends on others, and you must consider others in order to produce efficiently.
This has been really hard for me to accept, because internally my motivation is to follow my interests, and that is it. This is true for most scientists I think, especially after they finish graduate school.
But when you join a collaboration most people are interested in lots projects but they themselves are the lead on at most one or two of those projects. But they have excellent ideas concerning all of the projects. This is where the fundamental problem arises: how do you get people to contribute work to your project on your timescale?
What usually happens is you think of a project and start working on it. You tell your collaborators about it. You think of all the most important issues right away and deal with them. Then you start thinking of not so obvious issues and work on them. Then the work starts to feel like it's ready to share with the larger community. You must do this in order to be supported. You write it up and send it off to collaborators. For the first time, your collaborators start to really think about the project, and they have many good ideas. Most of them you already thought of but there are some ideas you have yet to address. Addressing these new issues often requires work from you, but it often requires a fair amount of work from the individual collaborator because only they fully understand it. So you end up delaying publication for a while, sometimes a long while.
If only everyone involved knew from the beginning that the paper would be released on an exact day, with no possible delay, they would have been forced to think about the project from it's inception in order to contribute. They would have realized that some input was needed from them up front. They would have done this work while you were working. Most of these issues would have been dealt with by the time the first draft was written.
Collaborating is worth while because I learn so much by seeing other people's perspectives. And everyone has such varied skills that the work is always better for it. The theory is that a deadline is an impersonal rule that once established should help to keep the ideas and work flowing more naturally and efficiently.