Using Humor Effectively
There's an old saying among professional speakers: "Question: Do I have to use humor in my speech? Answer: Only if you want to get paid!" This itself sounds like a joke, but the idea it represents is very serious ― most presentations will benefit from some degree of levity.
However, I say "most presentations" because it depends on both the seriousness and the style of your particular presentation. Remember that presentations range from conversational to theatrical. A serious theatrical presentation (like a presidential State of the Union address, or the CEO announcing company-wide layoffs) might not benefit from humor. But unless humor would be totally inappropriate in a particular situation, the judicious use of humor will allow you to establish a rapport with your audience that you can't do any other way.
Now humor doesn't necessarily mean telling jokes. (Actually, jokes aren't really a good idea except for professional comedians.) In fact, the best humor can be lighthearted. You won't get guffaws or even laughs from your lighthearted humor, but you may get smiles and chuckles.
Above all else, your humor should be natural. If you're not good at puns, stay away from them. If you're not comfortable with dry, deadpan humor, don't do it.
But if you're comfortable with any sort of humor ― exaggeration, understatement, witty asides, puns, sarcasm, or whatever ― your presentation will probably benefit from using some humor in appropriate places.
There are a few types of humor that you must be very careful with. Having fun at someone else's expense can be very funny... or it can cause a lot of resentment. Self-deprecating humor can be very powerful, but the audience cannot believe that you really mean what you're saying about yourself or their laughter will turn to sympathy and embarrassment. And telling jokes doesn't work nearly as well as it did years ago ― there's just too great a likelihood that your audience has recently heard that same joke on the Internet, and your funny joke falls flat.