Multi-vendor marketplaces, like ThemeForest, can be very successful. Chose a niche and create a vendor website for it. Your marketplace could be anything, from a platform for local artists to sell their work on, to an online digital product store. Once set up, invite people in that industry to sell their products on your site. You take a percentage of their profits when items sell.
Become an Amazon Associate and then use Keyword planner to find an in-demand niche: With more than a million different products to choose from and up to 10% commission the sales you drive, Amazon’s affiliate program is a great place to get started. Browse their available products and see what connects with you. Or take it a step further and use Google’s Keyword Planner to quickly check how many people are searching for a specific term. With affiliate marketing, the more relevant traffic you can pull in, the more you’ll make off your site.
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.