The courses that tend do best on Udemy are the technical type courses, particular web development, although a cool thing about Udemy is that they are open to you creating a course in almost anything, free market style. They have a large pool of students so you could get some extra exposure and quite possibly sales without any marketing on your part. Having said that, I’ve noticed that Udemy tends to reward teachers that do their own marketing by following up on the teacher’s efforts with promos from Udemy’s marketing department. It’s impossible to predict how well a particular course would do but if you are attracted to the idea of making a video based course and you have some time & knowledge to share, then it’s a nice project to do. If you treat the income as a bonus, you can’t go wrong. Good luck!