Humor is most effective when the joke or crack is relevant. A joke about confusion can help you make a point about restructuring the organization. A joke about poor service can help you make your point about good service. A joke about neatness says something about sloppiness. And jokes can certainly underscore or defeat a point.
Nothing makes something look as bad a making it look silly with a joke.
The audience does your bidding by laughing at your jokes when you want them to. Pepper your whole part with humor. There's no way an audience can be relaxed and receptive the whole time if you only tell them one joke. Humor Makes You Likeable - People are more likely to buy a program, a product or a point of view from someone they like. They warm to funny people.