Look at what the most popular courses are. If you see a ton of courses on a topic that has thousands of reviews, it’s a good idea to create a course on that topic. High competition means that it’s something people buy. Some topics are generally really popular for online courses. Courses on how to use Excel, how to make money online and how to lose weight tend to fare better than other online courses.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.