Number 1: Remember this above all else. The first rule of humor that I learned from the late Jim Samules: For every rule of comedy there is a comedian, humorist, speaker, trainer, presenter somewhere violating that rule and getting rich doing it. The bottom line is whatever WORKS for you is what you should be doing.
Number 2: There is a common misperception that in using humor you should open with a joke. Once again I say, "Baloney" - unless you are a humorist or a professional comedian. For two reasons. (A) You may be a terrible joke teller. There are many other ways to interject humor without resorting to jokes (and you will learn how to adapt the out-and-out jokes in Jokes Study at HumorMall.com). And (B) If you do use a joke well, but are not a humorist, your joke can mislead your audience into thinking that your presentation will contain a lot of humor (first impressions count the most) - - - and they can be very disappointed when your speech does not meet their expectations.
So, if you are not going to use a substantial amount of humor, I suggest not starting with a joke. You can use humor very early in your speech / presentation, but speak for at least 2-3 minutes before bringing in your first bit of humor.
Number 3: In the beginning stages, when you are trying to get comfortable with humor never use a bit of humor UNLESS it illustrates, clarifies, or specifically references the point you are trying to make.
This is called bomb-proofing you humor. People are like computers when it comes to humor. Computers are designed to recognize ONLY two bits of data: negative and positive represented in assembly language by '0' and '1'.
Likewise, your audiences only recognize two types of data: "funny stuff" and "all the other stuff." SO, if you tie your humor with the point and they don't laugh, they have simply classified the humor with "all the other stuff." Thus you continue your speech as if the audience responded appropriately. And you need not bother with what comedians and humorists refer to as "savers." (It does not make sense to use a saver on a "all the other stuff." )
Read these two preceding paragraphs over and over and over until you get the ideas burned into your mind. I wish I had someone make this vital clarification for me when I first started speaking (as opposed to doing comedy in a club). As a beginning speaker, I would have been saved from hours of agonizing on the platform about a line that didn't get a laugh. I wish I had realized then, that for that audience, at that time, and at that place it was not a piece of humor that bombed, it was merely part of "all the other stuff."
Addendum: In Should You Use Humor in Your Presentation I mentioned keeping a laugh journal. If you are new to using humor you might want to do this additional step. Try tracking the humor tool you used to make them laugh. I don't mean the underlying humor principle: exaggeration, wordplay, substitution, etc., or any of the many techniques covered in HumorMall.com. I mean the actual form or structure of the humor: Did you quote a one-liner you heard Jay Leno or some other comedian tell? Did you relate a funny bumper sticker you read? Did you recap a cartoon you thought was funny? Did you re-tell the funny thing your son, daughter, niece or nephew said..., etc.
If you are not familiar with your type of humor this is important because it will help you determine the form of humor you will be most effective with. And can also indicate if you should ultimately use props and audience participation in your presentation.