Brainstorm a bunch of actions and outcomes. Each member privately assigns an utility to each possible outcome, how likely they think each action is to lead to each outcome, how trustworthy they think each other member is on the question, etc. etc. Then you feed all of this into a black box AI algorithm and it outputs what action should be taken, which everyone simply has to take on faith until they have enough examples to take it on induction.
So my answer is the meta one of "I don't know, but whatever it is it'll be a complex or even downright inelegant, found through testing and interaction with the real world and/or simulations rather than armchair theorising or mathematical derivation from first principles, probably involve large datasets and some kind of machine learning algorithms, and not possible to implement well on a human brain".
So here's the problem: Given a well-defined group charter, how should groups make decisions? You have an issue, you've talked it over, and now it's time for the group to take action. Different members have different opinions, because they're not perfect reasoners and because their interests don't reliably align with those of the group. What do you do? Historical solutions include direct democracy, representative democracy, various hierarchies, dictatorships, oligarchies, consensus...But what's the shoes-with-toes solution? How do they do it in Weirdtopia? What is the universally correct method that could be implemented by organizations, corporations, and governments alike?
This Tuesday, I posted an idea. I came up with it about ten, maybe fifteen years ago, decided it was awesome and revolutionary, and spent a few years doing some extremely ineffectual advocacy for it. I've pushed for it in various contexts on and off since then, but I'd basically shelved it until I had a better platform to talk about it. And recently I realized, belatedly, that Less Wrong is probably the perfect audience. You're going to be open to it, and you'll be able to competently critique it. And maybe some of you will use it.
I posted this tease first because the idea is a solution to a problem you may not have thought for five minutes about. I want to give you the opportunity to come up with other solutions, or discuss how to rigorously evaluate ideas. Also, I'm really curious to see whether anybody independently reinvents mine. Over the years, I've had the experience several times of reading someone else's work and thinking they're about to start pitching my idea. But they never do. It all gives me complicated feelings.
Please discuss in the comments. Remember, we're aggregating the opinions, the judgment, of the group members, not their personal preferences. So answers like “iterated runoff voting,” “bargaining theory X,” or “coherent extrapolated volition” are not in themselves what I'm looking for. If you happen to know what my idea is, or manage to find it by google-stalking me, please don't give it away yet.