When you open your speech, work to get them to agree with you. It doesn't matter what the agreement is about, just get them to agree and so begin to build a bond with the audience. For example, you could say, "Have you ever felt disappointed in what you got out of your life?" and wait for the audience to respond in some way, either with putting their hands up, nodding, or some other way. Small agreements up front will help get them to agree to bigger ideas later on in your speech.