If you think you can control the audience. Could I suggest that you are mistaken? You see in the UK we have this thing called free will and adults have a lot of free will. They have the knowledge and experience to know if their time is being well spent in listening to you or indeed, anybody. The secret of getting them to want to stay is purely through engagement. What you're doing must be relevant to their needs and goals, otherwise it's a waste of their time.
Work hard. Stay on theme. Keep them engaged.