But don't make the mistake of thinking this will be a passive source of income—you're on call whenever you have a guest and you'll always need to keep the place clean for incoming visitors. On top of just renting on Airbnb, consider offering your guests paid add-ons, like Lauren Gheysens', Royal Day Out in London, England—where she gives visitors a local's only tour of the city, complete with bespoke 18th century costumes.
Write pitches. If you have located a client for whom you want to write, send pitches, which are topic ideas for articles. Write pitches that not only show your expertise, but also demonstrate your enthusiasm for the topic. First, read the publication to which you are sending pitches to familiarize yourself with what they publish. If applicable, identify a specific section and send our pitch to the appropriate editor. Also, include a brief summary of who you are.
If you are more confident in your skills, you can also market directly to websites and blogs. You can contact the sites by email to market your services. That will also enable you to select the specific types of sites that you are more comfortable working with. Since there are literally thousands of websites and blogs on the web, the potential market is limitless.
Drive for Uber or Lyft: If you're in a locale where you can find Uber or Lyft (or even one of the many competitors around the world such as China's Didi), you could easily make a respectable income. The hours are flexible and you can work as you see fit, making it perfect even if you currently have full-time employment but are looking to make some money on the side.
Find your niche partners, collaborators, and champions: As you’re creating your course, look for notable people who are also creating content in the space. Look at how their businesses operate and incorporate that into your own plan. You can also reach out to any influencers and make them affiliates for your own course. This way, they’ll be incentivized to share your content with their own audiences (which can be a major way to generate your first sales and start building your own community!)
Find a profitable niche. Starting with your interests, write down as many niche ideas as you can. Think about topics people might search online. Ideas include passions (like surfing or body building), fears (like spiders or speaking in front of crowds) and problems (like getting out of debt). Do keyword research to see it others are interested in the topic. Find out if a domain name is available that matches the keyword 100 percent. 
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.