You’re not the only fellow in the writing world. Like it or not. It’s a bare fact. The world is full of writers, much better than you and I. There is a whole lot of competition—in the print or online space—to attract readers. So I don’t mind shooting the 3ree most important questions at you—writers.
Is there a big market?
Nothing can be as rude as this for a writer, a poet or an artist to ask him/her if the work he/she plans will have a market. But this is today’s bizarre reality if you have, to a less extent, thought of selling your work in the market. Thus, it is a smart thing to do an analysis of the book you have planned.
Is there good demand in your market?
Well, it is even more audacious when you’re forced to look at market dynamics. Are the fellow authors selling well? Are people reading books, novels, stories, poems, fictional or non-fictional stuff? If there is no demand for your kind of book, it is obvious that you will struggle to sell it. Publishers will be averse to bet on your work.
How much competition is there?
Even if you would prefer to skip the previous two questions, you can not and must not skip this one. Competition is the most impeccable thing that decides the course of a trend in writing or painting or just any field. Better, if you’re familiar with the competitors as well as the emerging trends, before trying yours, and try to write different so that you give your readers a solid reason to pick you up from the crowd.
If you wish to ignore them, you can…but at your cost. Sooner or later you’ve to encounter them…this or that way.
O S scribbles... 
Good reflection! I wonder though—and I mean this in a naive, clueless sort of way—whether you have any tips when the answer to all three is “I don’t know”? And perhaps more importantly, how do you classify your own writing? For example, I like to write adult fiction, but “adult fiction” in itself is a huge market or category. Should I then divide it further into subcategories?
Well, to my understanding, when ‘I-don’t-know’ is the answer, an author is at a critical juncture to identify readers and weave his story further keeping the nature (assumptive nature) of his readers in mind. But I’d say the classification comes at a second place after when you’ve set out to telling a story.. I know you will have many justifications, queries and counter queries. But as an author, we want readers.