Let me start. I'll let my colleagues reflect a bit more.
Force them into some trade-offs. You have to do it. Find out what they value most. Come up with your series of principles, explain how they can work in comparison to others. I suspect that local representation will be very close to the top of the list. They'll want to know who their MP is. They want to know where you live, because it's that accountability and that possibility of throwing you out afterwards, the blunt democratic instrument, that's fine.
That would be one example that I think would jump up to the top, but try to force them a bit on that. Then, if you can, find out what they really want from an electoral system in this sense, and let me rip off what Elizabeth May said in terms of the central authority, the executive authority. Do they think it will cure this versus something else?
You may have a role in helping to address myths as well as improvements. Don't let the myths stand out there, that if we change the electoral system we can fix A, B, C, and D. Help them understand what those absolute choices are and help them appreciate where this is an improvement but not a panacea, if you will.
Off the top, that would be something that you could think about.