Humors effectiveness will always ride the emotional tides of your audience members. How well a joke goes over may depend on whose company your prospects are in, whether they are winding down for the day or still up against deadlines or other workplace pressures, whether they are awake and alert or feeling drowsy, whether they have a headache, etc. Always be in tune with how your audience is feeling and always assess the atmosphere youre in to determine whether it is conducive to humor.
There are a lot of factors that contribute to whether or not humor will be effective in persuading someone. Often, it will simply be the mood or situation that makes it obvious whether humor is appropriate or not. For example, if someone has just learned of a death in her family, you probably shouldnt start cracking jokes. Another example would be if you were speaking in a religious setting where there was an expectation that a certain degree of reverence always be maintained. You probably wouldnt go wild with the humor in this kind of setting. The appropriateness of humor for a particular setting or mood is usually not too difficult to discern. You just have to be observant. What may be...