You're going to have to be a good listener. Have questions prepared to get the discussion moving or restarted if it stalls, but also be prepared to generate new ones depending on what the direction the panel goes.
You can lead the panel discussions by mediating any disagreements, make sure that no one talks over each other and that everyone that wants to has a chance to talk.
You need to take whatever the topic is and lead with it then as you start the questions will begin and the entire thing will flow on its own from there, there is no easy way to do it.
