After you’ve built up a solid credit history by paying your mortgage for the duplex on time using your work income and rental income from the tenants, you will eventually be able to scope out another property. Get a mortgage on that, move in and rent out the other half of your duplex. Over time you can continue building up your holdings, but it will take years and years of grinding to start to make good income.
Research individual companies in your desired niche: If possible, it’s always better to become an affiliate directly with a company (if they have an internal affiliate program), as no one else will be dipping into your commission rate. This is the preferred route for most of the prominent affiliate marketers, including Pat Flynn. Unfortunately, it’s also the most work, as you’ll have to do the research yourself to see who offers programs (they’re usually listed in the website footer).
If you have an eye for design and some experience of creating websites, then you could offer your services as a freelance web designer. You will need to create your own stylish website, and have a few other projects that you can show potential clients to demonstrate your skills. You will also need to initially spend time emailing businesses to promote your services and find work.
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.
Getting businesses to advertise on your podcast, either at the beginning or end, or both, is a great way to create a revenue through podcasts. Most businesses won’t be keen to advertise on your podcast until you can prove a large number of listeners. Therefore, it is unlikely you will be able to start out from the get-go with sponsors. But once you accumulate regular listeners, or a high number of downloads from iTunes, you can start to sell advertising space on your podcasts.
Buy underpriced used books. Outfit a phone with an ISBN reading app, scan the ISBN numbers of books at used bookstores and thrift shops, and compare the asking prices with what the books are selling for on a site like Amazon. Whenever you get a good hit (which won’t be often but, since the process is fast, won’t take long, either), buy the book and resell it online. Be discreet about this, as the store managers probably won’t like what you’re doing.
Operate your business. Obtain the necessary business licenses and insurance. You may need to have an adult co-sign your public liability insurance documents or other documentation if you are under 18. Make sure to hire someone to manage your accounting. It’s important to know how your business is doing financially in order to make smart investments and stay in business. Advertise your business as necessary and ask clients for referrals. Network with other business owners to leverage your market share. Ensure you keep accurate business records and file and pay your business taxes.
Keep in mind though, you don’t need a website to do sponsored content since you can also get paid if you have a lot of social media followers. My wife has a pretty big Instagram following, and she gets all kinds of sponsorships. Not only does she get paid in cash, but we get a lot of free stuff, too. We’ve received free rugs, free lights, and free carpet cleaners. She only promotes things she loves though, so this strategy works really well for her.