First job of the moderator is to make everyone glad they are attending and looking forward to the proceedings. So first, bring some energy. Best one I ever saw was Clayton Christensen at American Enterprise Institute. In a couple of minutes we all knew he was REALLY glad we were there with him.
Second, if you can make a key distinction that makes the discussion fresh, new and more important, you are “teeing up” the subsequent speakers.
Third, protect your speakers. Questions coming from the audience are often not questions, and when someone feels the urge and right to vent, the target and the audience can’t do much. The moderator has to rip the proceedings back on track. Make it very clear you are there to honor the intention of the proceeding, which is why your audience came.