As always, a good engagement event depends on good planning. The first step is to identify what you want to get out of the event. By clarifying the aims and objectives, you will be better able to identify the people you need to recruit, plan the issues to be discussed and identify the best methods to gather the information from the discussion.
It is worth thinking about future engagement while planning. You may want to think about ways to keep in touch with the people you recruit to ensure you have a list of people to approach for future activity.