The action: Ask people to write down their own thoughts on paper before discussing an agenda item.
The long-form: You’ve given people time to think ahead of the meeting by writing a clear agenda (f40). But during the meeting, it’s the same people speaking all the time (*cough*extroverts*cough*), ignoring your suggestion to imagine a limited number of talking-chips (f40).
A good way to get a more equal participation in discussions is then to ask everyone to write their ideas down on paper first. “I’d really like to hear everyone’s views on this, so I’m asking you to first sit in silence for three minutes and write down what you think about the proposal”.
Hopefully you’ll also find that this reduces group think, since people can express their views independently of stronger voices.