Facilitation within the dreaming-planning-doing-celebrating phases
Facilitator could ask the person who arranged the meeting to state his goals for it (privately, some time before the meeting). The facilitator can then decide on which type of organization is the most fitting (that is, if we come up with different suggested guidelines for meetings according to their dreaming-status, planning-status, etc.).
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Possibility to ask again to participants after stating main goal (mentionned above) what they want to discuss during this meeting, to better organize time in letting people express themselves. Appropriate if goal is very vague and open. In this listing, don't hesitate to Interrupt: participants can often start to develop their ideas or reflect upon others, but this should be short: we simply want a list to manage time fairly. Also, when participants know the upcoming content of a meeting, they can auto-regulate themselves in speaking time and in what is appropriate to bring up (or so we hope... 
).
Guiding - how to interrupt, and when?
how - Doug's method of raising an arm quietly, showing he wants to talk, seems very efficient. As he is respected as a calm and good facilitator, the group usually automatically assumes that his point needs to be heard. Oder?
Showing disapproval: bad move.
when - How do we know when someone just took a detour to come back to the relevant topic or when they just drift away? Some people take a long, convoluted way to express their thoughts. How can we minimize the loss of communal time spent on expressing in 40 minutes an idea that could be explained in 5? Unfortunately I don't see a great solution: cutting them off repeatedly has negative consequences both for speaker and facilitator and can easily lead to tensions between the two. But if the speaker keeps on taking too much time and thus indirectly cutting off other people, the facilitator should do something about it. But what?
Getting to know the individuals and how they express themselves seems to be the first condition to solving any of this. Then and only then, the facilitator can choose to have a private Chat with that said person, using the uppermost tactfullness to explain that something has to change. Something like "You have great ideas but it seems that the way you express them makes it difficult for people to really grab them. Would you allow me to share with you some methods I learnt for a more efficient communication?" (but really, I should never be a diplomacy teacher). What are These methods then? "Golden rule: deep listening. That means we respect each other and we don't interrupt one another. Focus on what someone is saying until they have finished, Close your eyes if needed. Eventually you may find that this eases up the very process of talking, yourself. By assuming that others listen as deeply as you do, you may not feel the need to rush into unorganized thoughts anymore." And indeed, people will understand and remember much more clearly a slow speech that goes straight to the point than a fast one that gets lost on its way. But frankly, this whole Piece of advice might only be relevant for the couple of People I have in mind as I'm writing this. Which brings me back to my main Point: know who you're dealing with before