If you're interested in online marketing, setup email software and create a lead magnet that you can use in your sales funnel. Then, build up that list. It's often said that you can expect to earn about $1 per subscriber per month. If you have a list of 10,000 subscribers, that means you can earn roughly around $10,000 per month. You will need to deliver value and not pitch them on every email, but it is a very achievable goal in a short period.
Whether it’s an important consumer application, a specialist app to solve a particular niche problem, or even a time-wasting game you can play on your phone, you can create a massively successful business if you build software that helps people. (Look at the rise of Slack—the team communication software that went from side project to billion-dollar company in just 2 years.)
A spin-off for web designers is to offer a landing page creation service. Well-optimized landing pages can be the difference between a successful and a failing business. And, as creating the perfect landing page isn’t easy, this is a service many businesses are prepared to pay for. I know people who are earning 6 figures per year and all they do is create landing pages for businesses. There’s serious money to be made.