Premium content can mean any type of content you charge for - an ebook, whitepaper, downloadable guide, etc. But what I'm referring to here is pay-gated content. Basically you just put some awesome content up behind a paywall, which means visitors pay to access it. You can get your own paywall set up in 10 minutes or less using a plugin like MemberPress or Paid Memberships Pro.
If your niche doesn’t allow you to promote or build premium products (anything over around $100 per unit) then think about getting a solid mix of offerings and building it up over time. I remember Darren Rowse saying that initially Amazon Associates was a really small source of income but over the years it has really started to add up. Think eBooks, affiliates, consulting, books, etc. and you’re starting to build an income stream.
One example is this: since our blog is a sub-domain for my wife and I’s boutique beach resort, nobody seems to want to touch me as a guest blogger. I get the same response every time “you’re commercial and so you’ve got to pay for a sponsored post”…and while yes, we are commercial and not a private blog per se, we’re a tiny family run business and 95% of private blogs are striving to be commercial, whether they’re associated with a company name or not.