If you have a good idea for an app, and the skills to create it, then producing your own premium app can be profitable. However, with so many free apps available, it may be hard to convince people to pay. If you want to go down the premium app route, consider having a basic free version to encourage people to download the app in the first place. You can then provide the option of upgrading to a premium plan once users realize how useful the app is.
Build up a following on your Instagram account and you could quickly be making extra money online. Major brands, gear companies, and even startups are willing to shell out $500-$5,000+ per post to get in front of your audience. While it’s getting harder and harder to build a massive Instagram audience, if you already have a solid niche and are posting quality content regularly, with a few small tweaks you can make yourself an influencer. Check out this awesome article from Shopify on how to build and grow your Instagram following to get started.
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.