Many people who send out promotional email, or have a publication such as an online newsletter, will ask if they should include 'humor". Well, there is no easy answer to this question.
Some will say that "humor" lightens things up a bit, and lets people know you have another side to your personality. They feel it is a refreshing break from serious message you are delivering. Others say it is distracting and should never be used.
So where do you "draw line"?
Humor can be used in two places. It can be within body of article or as a "stand alone" item.
Let's first examine "humor" within body of article. This can be most risky. Unless you have a good sense of humor and good writing skills, you should probably avoid its use. Some of your readers will not have a sense of humor, and could easily take offense at what you say. Especially avoid sarcasm as people may think it is directed at them.
You should also avoid use irony, where you use words to convey opposite of their literal meaning. Some will not recognize it as irony, and will think you are proposing what words actually say. This can get you in a lot of trouble.
If you use "stand alone" humor, give it a title such as "Joke of Day", which clearly separates it from your article. Once again, you have to be careful. Remember, your online publication is on "world-wide web", and will be read by people who may have far different opinions of what is funny and what is not.