Latch on to a popular service, then simplify it for others. Self-described “professional nerd” Brett Kelly wrote Evernote Essentials, the first English-language manual for the popular Evernote software. Brett was hoping for a $10,000 payday over the course of a few months—enough to pay off some bills. Instead, he received $10,000 in two days… and then the sales kept coming.
cc. David Perell's tweet about building a brand around a popular new tool where he cites Marie Poulin and Notion.
Countless examples of this: Nat Eliason, Shu Omi etc. with Roam Research.