One of the best markets these days is writing for writers. It's a solid money market. The source material is available everywhere for the legitimate taking (properly quoted research). There is virtually nothing that has not been written about how to be a successful writer. It is a phenomenally large market and virtually credential independent if you have a good enough hook (idea that catches the reader's attention). Writers do not buy how to write books only from famous writers. Famous writers are not always great teachers. A chess grandmaster once told me that if I wanted to be a successful chess player I should not ever study with a grandmaster. Great players, he told me, are generally poor teachers. He was right and it applies to writing instructors as well. But you are not a successful writer yet? Well, you don't have to be. Are you a good and honest researcher? That's enough. Here's a solid fact- you do not have to be a successful writer yet to make a good income from telling other writers how to write. Just do the research. Interview other writers and include their commentaries and stories in your book (properly attributing them, of course). From there you could be off to starting your own YouTube channel instructing writers how to write. Think about it. Most of the successful food writers are not great chefs. They are great food researchers and interviewers and they write about what they learn. You'd be surprised how many successful writers will be glad to be interviewed for your book on how to write. Writing for writers about how to write has its origin in the network marketing industry, where most of the money big distributors made was through books and tapes they sold newbies about how to be successful distributors. As in the case with most writers, the average income from those ventures was well below the poverty line except for those distributors selling books and tapes about how to be distributors. Did you ever wonder why Dale Carnegie- a mediocre writer at best- made so much money? Well, it's actually fairly straightforward. He wrote books telling other people how to make money! (semi-kidding). But he had tapped into an unbelievably rich strain of making money as a writer. Telling other people how to do what they want to do. Writing is, for the majority of writers, a terrible way to make a living. That's why there are so many books sold telling writers how to write successfully. The demand is never ending. And as you write for the writing for writers market, you really will learn a lot about the craft. The content of these "how-to write" books is endlessly recycled as if it were fresh. I have over 400 "how-to write" books and I quit buying them 20 years ago. I'm a sucker for how to write books. Most writers are. The writing for writers market is bigger than ever and you'll learn a lot about writing in the process. A lot of this is tongue-in-cheek. My publisher once advised me, "Quit reading about writing. Study the writing you love, dig out how those authors did it, then get to work and writer your own stuff. Quit feeling inadequate and write." It got me moving.