Some humor 'experts' say that you should not laugh at your own jokes and stories when you are speaking in public. This may work for some, but it is definitely not my style. When I'm in front of an audience, I'm having a great time. I'm there because I love humor and laughter and I love sharing it with the audience. I can't help laughing sometimes. I laugh at what I say. I laugh at what they say. I laugh at unexpected occurrences during the presentation. That's my style. I believe that to fully connect with an audience, you must be accepted as one of them. If I expect them to laugh, then I should laugh too.
Sometimes you can laugh to tell the audience it's time to laugh. Within a matter of minutes your public stage persona will be evident to the audience. As soon as they catch onto your style and rhythm, they will pick up on the cues you give them. When you laugh, they know it is time for them to laugh. It's almost like holding up an applause sign. Some presenters use facial expressions or gestures or a combination of many cues that tell the audience it's OK to laugh.
The opposite of a laughter cue is a deadpan expression. This is a serious expression that is contrasted with funny lines. The contrast evokes a larger laugh than the line could get by itself. I use this to set the audience up for some fun questions. I look completely earnest when I say, I'm the foremost expert in the world [pause] on dumb questions. It always gets a good laugh.
When speaking in public go ahead and laugh when you feel like it. Both you and your audience will enjoy the speech more.