As I wrote previously, your audience is a superb resource for new material. But here is a caveat about audience humor. Sometimes audience members will come up to you after your speech and share a bit of humor with you. Often they will say, "You can use that if you want."
This well-meaning offer of material can sometimes be a source of good material, but it can also be a source of humor that will embarrass you.
Here's what to look out for when it's definitely good and/or helpful. When someone comes up to you and says, "When you said, 'such and such', I thought you were going to say 'thus and thus'." In cases such at these, what you have is an unpaid comedy writing collaborator who has possibly just given you a better set-up to your humor piece, a better punch line to your humor piece, or an additional laugh line.
In that case, use the material if it fits you, your slant, and your sense of humor. Or adapt as needed to fit you, your slant, and your sense of humor. But when someone says, "Let me tell you what happened to me (or their spouse, or child, or neighbor) . . . " be a bit leery.
This is where you can embarrass yourself. Because often, the story they tell you is not something that really happened to them or an acquaintance, but rather often is a story in public use with some embellishment. Maybe something they're embellishing themselves or perhaps something they believe to be true because someone they love, respect, or admire told them it was true.
But, it could be an anecdote in public domain that has been embellished to make oneself more interesting or attractive to a friend, lover, or cocktail party listener. And the embellisher figures, hey what's the harm?
Well for the amateur, nothing. Who is likely to find out and what is more important, who cares? But if you, a professional giving a speech, take an amusing tale, adapt it to your presentation, present it as your story (or as an integral part of a vignette) and it is actually a story that some of your audience members are aware of as being in the "public domain," you may lose some major credibility.
Even if you preface your story by saying, "A woman/man in my audience told me this about his/her experience," you can lose credibility with any audience member who recognizes it. Now having said that, I do believe you can get good material if you take a few simple precautions.
First use common sense and intuition. Does it sound fresh or do you have a nagging bit of doubt that it is not entirely new and/or original? When in doubt, throw it out.
Secondly, ask four or five of your well-read friends if they have ever heard of it before. Especially the people you know who always have a lot of funny stories at hand. Or the person who's read ten or twenty humor books and seems to have a story for every occasion. If they haven't heard it, while I wouldn't say it's 100% safe, your odds have been increased a lot. And finally write it in such a way that you can't be hammered if others do recognize it.
I have a funny, funny talk, believe it or not on my cancer diagnoses and cancer operation ("Living and Laughing With Cancer"). After a talk at Mt. Zion hospital, here's what an audience member said to me, "A friend of mine’s husband was scheduled for chemo treatments and she had her hair cut off and head shaved in moral support of him - and NONE of his hair fell out!"
Next, you'll read what I did with that line to make the story more full, to make it more visual and dramatic, and to get a big laugh with a better constructed way to deliver the punch line.