Answer:
The main thing to do is to decide your main idea and then to develop the points you will discuss to help the audience understand. Good seminars help people transform their thinking processes and adjust their actions. Audio visuals, group activities and limited breaks will get you there. Then--practice with several small groups and ask the people to write evaluations. That way, you will be able to make the changes you need, replacing the ideas that don't really work with an audience.