Every presenter has an obligation to meet the audience's expectations. In this regard, you are like a singer or a musician who is hired to perform. The audience may not be paying you in currency, but it is paying you with something more valuable—its time.
On the simplest level, audiences expect a presenter to show up on time and finish on time. Most speakers have no problem with the first part; it is the second part that can be troublesome. If you are asked to speak for 15 or 20 minutes, aim for 18 minutes. The audience will love you for it. I have yet to hear an audience complain that a speech was too short, but I have heard plenty of complaints about presentations that seemed to go on forever.
Keep in mind that you are speaking at the pleasure of the audience, not your pleasure. People can get up and leave at any time. Most of them will not do so, but they always have that option. Bill Veeck used public speaking as a tool to drum up interest in his ballclubs; he would speak anywhere anytime if he thought it would help sell tickets. But Veeck didn't just show up; as a natural raconteur, he provided entertainment in the form of great stories, often at his own expense.
Audiences expect presenters to be prepared. If you are a salesperson, know your product or service better than you know the floor plan of your house. Likewise, if you are a guest speaker, be current on your topic. Know of what you speak. Keep in mind how prepared Colin Powell is when he gives a briefing; he knows the facts cold. The same is true of Rudy Giuliani. They are leaders who know the issues and can speak to them.
Audiences expect presenters to talk to them, not at them. If you are delivering a call to action, invite the audience members in. Don't order them to act. If you are preaching a message, speak as a member of the congregation, a sinner like all the rest of us, not as some anointed prophet. To paraphrase an old saying, "You will attract more followers with an acknowledgement of personal weakness than with an attitude of self-righteousness." One of the most saintly humans of modern times, Mother Teresa, never spoke of what she was doing for others; instead, she always invited people to share in the work that needed to be done for others.
And finally, audiences expect messages that are in tune with their wants and needs. Salespeople need to meet this expectation exactly. Others, however, can deviate somewhat. Often the presenter must deliver a tough message about hard issues, e.g., a corrective measure, a quest for improvement, or the big one—the need for change. Messages like this make us feel uncomfortable, so it is up to the presenter to find a way to make the message amenable without changing its content. A sure way to do this is to appeal, as Washington did, to a shared past and an attitude that "we are all in this together."
It is necessary to point out the difference between relating to the issues and pandering to the issues. Relating implies empathy; pandering implies playing to. For example, when Lyndon Johnson spoke about his plans for the Great Society, he touched upon his experiences as a poor boy growing up in Texas. He said he understood what it meant to have very little and how important government assistance was to those who had nothing. His themes related to the themes of those he was trying to persuade. By contrast, Joseph McCarthy stirred Americans' fears of communism by playing to their baser instincts of hatred and exclusionism. He lowered the level of debate rather than elevating it.
When you relate to an audience, you do not need to tell it what it wants to hear. You strive for the truth, but you present it in a way that is credible and understandable. At the same time, you need to avoid preaching or talking down to the audience. Both can be equally irritating to an audience.