Plan your speech with the time of day in mind, and use humor advisedly. Opening your talk with humor at 7 or 8 a.m. is not a good idea, according to Tom Antion of Great Public Speaking. Not only would it likely go over badly as it did for him, but could shake the confidence of the speaker, if he or she doesn’t realize that the reason is probably the time of day, not the joke.
On the other hand, humor can be very effective (if planned, audience relevant, tested, and not offensive in my view) and especially helpful for after lunch and evening sessions. Tom had another post several months back on the use of gags that I particularly liked. He relates a story he told to get his audience’s adrenalin flowing. He recruited 10 good-hearted attendees to agree (before his talk) to do a mad dash for the exits during his speech when he “grimly” mentioned (after being handed a note by his assistant) that an irate husband was on his way over to find out who was there with his wife. He tells it much better than I, and has a couple other gags you may enjoy. Take a look.
Since speaking is still one of the best legal marketing tools, it is important to not wing it. Planning and practice (no matter how many times you’ve given the speech) will make this business development technique much more effective.