I highly recommend that when you run an ideation workshop one person is designated as the facilitator. What does this mean? 

A facilitator is someone who engages in facilitation—any activity that makes a social process easy or easier. — Wikipedia

The facilitator is basically the person who will lead the workshop. As the workshop leader I often recommend that this person isn't also generating ideas. Especially if there is a voting and prioritization exercice in the workshop. You can't be player and judge at the same time.

But what does the facilitator do? Here the key tasks of a facilitator:

1. Introduce the exercice: explain what the process is and explain every ideation exercice

2. Keep the timing: nobody likes to respect a timer, the facilitator serves as a social pressure to have a healthy time contraint that helps stay creative

3. Coach: help the people who are lost during exercices

4. Adapt: feel the participants and the process and know when the plan needs to be changed to arrive to the defined goal