Create just enough constrains to reach meaningful outcomes.
Not too many to restrict creativity. Not too little not to reach a result.
Balance involvement, track discussion towards a goal.
Facilitate space for people to hear each other.
For me an eye opener was a book called: Facilitator's Guide to Participatory Decision-Making from Sam Kaner. Do not let the name of the book confuse you. This book is all about the things I have mentioned above and much more. I use it every day.
What do you use to engage people to work even more productively together?