Humor has very little place in business writing, just like erotica or violence.
The reason for this is people are not generally in the frame of mind, when consuming business writing, for anything but what they are trying to learn or understand. Sitting in a club or theater or at home watching TV, they are expecting humor, or erotic love scenes, or fighting.
When they are expecting entertainment they will enjoy it and accept it. When they are expecting facts, analysis, conclusions and/or guidance for their business or legal situation, they don't particularly like anything else, it creates cognitive dissonance.
That said, the key thing to know about humor is that there is generally an in-group and an out-group defined by a joke. Jokes point out something ridiculous; derived from the word "ridicule." So many jokes are pointing out something stupid somebody else is doing. The set of people being ridiculed is the out-group, the set of people laughing at the ridicule is the in-group.
Jokes tend to be naturally divisive, except in one circumstance: When the person being ridiculed is yourself or your group. That is self-deprecatory humor; e.g. how you are so bad at reading maps it took you ten minutes to figure out this restaurant was next door to your hotel.
Otherwise, it can be extremely difficult to be certain that your out-group does not include any members of your audience. It is not a good idea to start ridiculing members of your audience!
So you have to exclude from your joke material anything that you cannot know about your audience, including their personal characteristics, or characteristics of friends they care about. So nothing about sex or homosexuality, religion, disabilities, national origin, prison, politics, and on and on.
Further, business writing (like in a book or lesson plan) may be an evergreen essay; so nothing about current events, or cultural references that won't be relevant or understood in ten years.
It isn't impossible to find humor in business, but the good spots are rare, and you should avoid ridiculing anybody but yourself, or perhaps your own fictional characters you used for illustration, but even those are not safe: Some of your audience members may be identifying with the Paul the Plumber character you invented, and not appreciate you ridiculing choices they too might have made.