Using Humor
Beginning a presentation with a joke can be an effective strategy for winning over one's audience, provided the speaker or author knows his or her audience well. However, the speaker better hope the audience thinks the joke is funny! Most often, keeping one's joke clean is prudent, as not to create discomfort among the audience. Also helpful is telling a joke relevant to the subject being presented. Here, for example, is a joke one might use for a presentation on football: Anyone who makes a bad call against the Detroit Lions risks ticking off their last remaining fan!
Take care with the subject matter as sometimes humor can do more harm than good. If you decide to use humor at any point in your presentation, it is a good rule to avoid all sexual, religious and racial topics or references.
Irony and metaphor
Two common rhetorical devices used to convey special meaning to an audience are irony and metaphor.
The use of irony in rhetoric is primarily to convey an incongruity, often used in humor to deprecate or ridicule an idea or course of action. When taken in context, the statement may actually mean something different from, or opposite of what is said literally.
Irony
A stop sign ironically defaced with a beseechment not to deface stop signs
The use of metaphor in rhetoric is primarily to convey a new idea or meaning by linking it to an existing idea or meaning with which the audience is already familiar. Linking the new with the old and familiar through the use of metaphor is an excellent tool for introducing new concepts to one's audience.