Whether anyone will read it or not, shouldn't enter into any part of your process.
You suggest you might be a fiction writer. What sort of fiction? I have seen around 20-30 genre . . . One size does not fit all.
As they say above, first you must be inspired. All the perspiration in the world will not help to compile a book unless you have at least some glimmer or tantalisation, as someone says, to build and compound tension.
My pet subject in my subset of genres, MTS, Mystery, Thriller, Suspense and Action/Adventure I believe are all about HOOKs. To me, there has to be a HOOK on page 1, maybe even paragraph 1. Could even be sentence 1.
That doesn't mean you have to get formulaic, or follow everyone's pattern of writing. IMHO, a good Action book has several hooks which means several climaxes. Now we all know what a good climax is worth. Having multiple climaxes, IMHO, is the real way to make people happy, truly happy.
In my way, I want the reader to KNOW they have read one of my books. I sort of want my books to be interactive. I want readers to yell at the book, yell at the movie and TV screens, yell at the blind person who is reading my works, so to speak.
So my approach is quite passionate, at least, in my own way I think I am. I have written a series, some 20 completed books, averaging 80k+ words each. If you see the style that JK used with HP, I may have been influenced by that style, at least it appears that way to me. My series is almost like a journal of his activities over a three year period.
My concern is that certain events in place now, may automatically morve the MC's life ahead and I may move out of the prime 'time' of his like that I like to write about.
So as Harry grew up in front of us, I am trying to more of a James Bond way, or Sherlock homes way where they just exist almost in one day, month and year. As the author give up ant aging of the character or members of his team.
Anyway, you wanna know what to write next? What is gonna work and be popular when it is published?
I agree with Jayce:
"whatever that hot idea was when you began has long since been abandoned by your mainstream audience"
So, #1, I write for me.
If it doesn't give me my jollies, then I don't believe it will appeal to others or many others.
#2, Unless it is a good or great base idea, I won't even note it.
If I have any skill, it is that I get a good base line concept, someone to attack, some political strife in a real or mythical country and then all the subplots fill themselves in as I go along. I never have to be concerned with the word count. Altho I fall short occasionally, mostly it is what it is and that is over 80k words. My rule of thumb for my writing.
I have no idea if my books will be published, then, if they are, whether they will make money or not.
I write for me, and that is what I want to share with others.
Kylie, go write something. Long, short, middle of the road. Send it to me and we can discuss it privately or publicly. What is your target market?? Genre, age groups? What appeals to you as a writer?