The key to being an effective public speaker is to not assume you know what the audience wants to hear. The author suggests giving up Power Point presentations, that it makes the assumption that the audience wants to learn the same way you do. He suggests to talk less and listen more, making time for questions and answers to let the audience learn from each other and not just him. This approach opens up to letting the presentation go on for as long or as little time as the audience needs to learn what the speaker is talking about.
Read more: The Key to Being An Effective Public Speaker