Your niche doesn't necessarily need to be an area you're already an expert in. You can also choose a specialized area which you're enthusiastic or interested in learning more about.Think of Oprah, she doesn't market herself as an expert, but she frequently brings other experts on her show. You can do the same in your niche, by giving other experts a platform to promote themselves in exchange for content creation.
If I have a blog that is getting 100,000 page views a month that means that I’m probably getting at least 50,000 people to the site (most blogs will do between 1.2 to 1.4 pages per session). That means I have to try and get some small percentage of those people to buy something from me if I really want to do well. If I can’t get them to buy something then (in some cases) I have ads running on the site that will make me money anyways.
Etsy: While Etsy's popularity has declined recently, it's still a great resource for selling handmade items online. No need for complex ecommerce sites or merchant accounts or any sort of automation. The company takes a commission of every sale and charges a small listing fee per item. But many still use Etsy as their primary source of income. The best part is that you can also sell digital products on here such as poster designs.
If you’re looking for inspiration, my friend Michelle Schroeder-Gardner of the website Making Sense of Sense has become the expert on all things affiliate marketing. Michelle earns more than $100,000 per month from her blog and the bulk of her income comes from affiliate sales. Michelle has had so much success with affiliate marketing that she even has her own course called Making Sense of Affiliate Marketing.