Jeremy Donovan's study of TED talks suggests your speech will go better if you use the opening of your speech to "feel out" your audience's energy. Ask a question, see how people respond; or callback to something the audience has already heard; or get a laugh with humor relevant to your topic. Do something that helps you understand where the audience is and what you will have to do to take them to where you want them to go.
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com