Agree on a theme for the meetup and select the panelists accordingly. Send an email to all attendees asking them to come prepared with questions and challenges. You should also prepare 2-3 probing or controversial questions for the panel to get things started.
If there is a lot of active discussion from the audience, you may change the meetup format from Panel to Fishbowl.
Setup rows of chairs (auditorium style seating) facing the front. At the front, place one chair per panelist, and optionally one chair for the moderator (host). In most cases, however, the moderator will remain standing.
Spend a few minutes introducing each of the panelists, including; who they are, their experience, and what they bring to the discussion. If there are pre-determined disagreements or differences of opinion, share these with the audience. This will help them ask relevant questions.
If there are no immediate questions, ask your first question. Let the panelists respond. Timebox each question to about 5 minutes and go back to the audience. Ideally you should never have to ask your 2nd or 3rd prepared question.
An important note, not all panelists have to respond to all questions. It gets very boring if someone asks a question and each panelist takes a turn to answer.
Send an email to everyone thanking them for joining. Send out any slides from the panelists if relevant. Remember to invite them to join the Business Agility Institute.