If you're serious about making money online, start a blog. Blogging is one of the easiest and most sustainable income sources. As long as the blog is setup the right way, in the right niche, with the right content targeted at the right audience, and the offer is complementary to the content, you could make a tremendous amount of passive income from a blog.
Now, if you don’t know people who might want your coaching services, there are a number of online tools and communities that make it incredibly easy to find clients and teach, on just about any topic area you can think of. Community driven platforms like Savvy.is, Clarity.fm, and Coach.me provide you with a network of potential clients to interact with, as well an integrated payment solution.