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.
Use the law of supply and demand to your advantage. Most of us are familiar with the law of supply and demand--the more there is of something, the cheaper it is; conversely, the rarer the product or service, the more expensive it is. However, other than when we get to a toy store before sunrise to get on line for the latest fad toy that kids can't get enough of, we don't really apply the law of supply and demand to our own lives--particularly our careers. For example, if you're aspiring to do something that many, many other people want to do (so much so that they do it for free, as a hobby) then it will be far more challenging for you to make money doing it. On the other hand, if you do something that most people don't want to do, or if you get very good at doing something most people don't do all that well, then you can make a whole lot more money. In other words, choose a career in pharmacy over photography.
Teaching and tutoring English as a second language is a great way to make money online, not to mention open some doors for you to travel the world if you'd like. While full ESL (English as a Second Language) accreditation is recommended, as long as you’re a native speaker and have the ability to teach, there are people in countries such as Hong Kong or the UAE who are willing to pay upwards of $25/hr for you to tutor them English via Skype. Check out Indeed, Learn4Good and Remote.co for remote english tutoring jobs or sign up on a specialized site like VerbalPlanet or Chegg Tutors.
Creating a video series and selling it as a digital download on your blog, much like an eBook, can be another great seller. A video course, teaching viewers a specific skill or how to achieve a particular activity, may well resonate with your audience. If you are going to go down this route then your videos need to be as professional as possible so you should consider investing in some video and lighting equipment, as well as editing software.
Here’s a good example of how lead sales can work in real life: My second website, Life Insurance by Jeff, brings in a ton of traffic from people who are searching the web to find answers to life insurance questions. While I used to have the website set up so I could sell these people life insurance myself, it was a lot of work to process all the different requests and clients. As a result, I started selling the leads I gathered instead.