If you pose as somebody you're not, your audience will know you're insincere and therefore disbelieve whatever you're saying.
For example, if you're naturally a casual person, you'll seem gawky and untrustworthy if you try to be formal. Similarly, if you're naturally strait-laced, you'll come off as foolish if you try to be "cool."
The same rule applies to expertise. People sense it right away whenever you pretend you're an expert if you are not. Rather than attempting to borrow credibility from your business card, be the person you really are. Only then will you be believed.
2. Tell stories.
The purpose of a presentation is not to convey information. You can do that with a data sheet. The purpose of a presentation is to show how that information has meaning for whatever is going on in the businesses and lives of the members of your audience.
Human beings decide what's meaningful on the basis of how something fits (or doesn't fit) into the stories that their brains are constructing from their experience of life. It's only by telling a story--their story, in fact--that you can give meaning to your words.
The very best public speakers make it seem as though the ideas are so new and original that the speaker is slightly surprised at what he or she is saying. Steve Jobs had this improvisational flavor down to an art. (So does Ron Popeil.)
The only way to achieve this "eternal newness" is to rehearse your presentation to the point at which you transcend your script, and the ideas it contains become part of who you are. By contrast, even charismatic speakers are tedious when they wing it.
Audiences consist of individuals. Because of this, talking to "them" is always a mistake, because it diminishes those individuals into part of a crowd. Great presenters always direct their words to individuals, moving from person to person.
This is much easier to do if you know some of the people in the audience as individuals. Therefore, it's always a good idea to arrive before the presentation to meet and greet audience members, ask questions, and learn who they are.
As a general rule, no presentation should be longer than a half-hour and no presentation should ever run over its scheduled time. Above all, never cram a full presentation into a five-minute window. Create and rehearse a four-minute version instead.