Have you ever sat in a seminar or listened to a speaker try to make a joke that came out wrong or was just ridiculous, not funny at all, and you were actually embarrassed for them, even glad it was not you making such an error in Judgment? I think we all have, this is why I recommend that you learn a little bit about the basics of humor and the philosophy behind it, as well as the fundamentals, techniques and most importantly the timing.
If you are serious about being funny, when it really matters, then it behooves you to brush up on your skills a bit. Joining Toastmasters is a good idea, do not get me wrong and getting over your fear of public speaking is paramount, but telling a good joke at the right time is paramount to effective speaking. Let me recommend a very good book to you, one which has helped me become a great public speaker:
"The Executives Handbook of Humor for Speakers " by the Bureau of Business Practices. 1971.
Now you may say, well this is only for business purposes, and well, you could say that, but if you would have been extremely short sided. Indeed, I have given speeches to large groups before on all sorts of topics, from crime to environmental issues. Each time, I found that the words of wisdom in this book had helped me put the crowd at ease, put them in a good mood and opened up their minds for discussion and dialogue.
When you use good humor, you set a positive tone, and that is true whether you are talking to a small group of friends or into a TV camera with 40 million potential viewers, so consider this book to help you become a champion of humor.