I write about all types of subjects and I have my favorites: business, relationships, eating out, heaven and hell, the Grim Reaper, prisoners and desert islands. Gags on these topics are pretty easy for me to write. However, sometimes I'm asked to write about subjects I don't have that much knowledge of, for example, biology, farming or horse racing. When that happens I have to do some research.
Usually, making a list of words off the top of my head that relate to this unfamiliar topic is not so easy and doesn't give me great results. That's when I need some help. I can try using the Internet to find words and phrases about the subject. Another idea is to find a magazine or book which deals with the topic (I spend lots of time in the library and take out books I can read at home). Anyway, I study these magazines and/or books and jot down words and phrases that could be used in writing gags. A lot of times this is boring if I'm not interested in the topic. Other times it's baffling, because I don't understand the topic. That's when I wish I were writing about business, relationships and eating out. But ultimately I plug away and do what I have to do. If the subject is technical and boring to me, many times the end result is that I won't write much worth sending to anyone. It's just not easy for me. That's when I have to revert to the simplest words and phrases, which is what I came up with before I read the magazine or book.
You do what you can do.
I must say that I've surprised myself many times as I've come up with gags about topics that I never wrote about before. When you try writing for new markets you'll soon find out what works and what doesn't. What's easy for you. And, in the process you might find a whole new area of writing that you can be great at. Anything is possible.