Next, you’ll need the right tools. You can be as complicated or simple as you want depending on your comfort with audio equipment, but at the minimum you’ll want a microphone and software for recording your voice. Companies like Behringer, Blue, Focusrite, and others sell studio-quality plug-and-play podcast setups that can get you recording today.
Even if it’s a mundane task like walking dogs, you could start the next (or only) full-service dog walking and grooming service in your town, where dog owners rave over your business and always refer you to others. You can hire other dog walkers as you grow, and turn your side hustle into a sustainable enterprise. You just have to do the work, and do it well.
Furthermore, carefully consider your likely attendees, and what schedule would be attractive to them. For example, if you’re planning on teaching a tutoring class, you obviously couldn’t schedule it during school hours. Likewise, a class aimed at mothers of young children will either have to include babysitting services or be scheduled at night, when they’re more likely to have help with the kids. Find the delicate balance of times that fit your prospective students’ schedules as well as your own.
It's NOT easy, but it is very profitable if you know what you are doing. And yes, there is a good potential for passive income. I find most Internet Marketing coaches are bogus, and just want your money. I learnt from someone of very high integrity called Eric Holmlund and he offers is teaching 100% free. His main angle is marketing digital products. I wrote my impression of him and his tips here if you're interested
Whether you have a website or are still dreaming up ideas for a blog, you can also look into affiliate marketing. With affiliate marketing, you partner with brands and businesses within the content of your website. If you mention a product or service, you link to that produce or service using a unique affiliate code you received when you signed up for that particular affiliate program. From there, you’ll make money any time someone buys a product or service through your link.