Nominal Group Technique
Silent Writing Members generate ideas before comparing with others.
Share ideas but do not debate them. 
Each person gives one idea then the next person gives one idea and so on, going around the circle until everyone is out of ideas.
Low status introverts speak first, leader goes last or not at all
Merge similar ideas but do not debate them; 
If A can stand alone but B only makes sense with A,
have "A but not B" and "A&B" as two entries on list
Do NOT eliminate silly ideas since this requires debating which are and are not silly, and it's not time for that yet!
Discussion Compare ideas and debate their pros and cons. 
An idea is good or bad as is is helpful or harmful (or simply useless) with repsect to one or more SPECIFIC OBJECTIVES.
(Note debate is NOT allowed before the discussion stage!)
Voting Secret ballot helps avoid groupthink or "Abilene paradox."

Note that the nominal group technique can be used at various stages of decision making, depending on what the "ideas" in the table above refer to. 
You can have one nominal group session to decide on the Problem scope and definition,
another to decide on Objectives or "measurables,"
a third to decide on a list of Alternatives to be considered. 
The Consequences phase is probably the least suited; Delphi is ideal for this. 
But nominal groups could be very good for the Tradeoffs phase.