Children's picture books started me off in the publishing business, but I also write poetry and non-fiction, especially in my journals. Last week I sketched out a non-fiction book which will be (probably) my fourth publishing effort. It will be a small, hand-held book for teachers which will be easy to read, easy to pick up for reference. The rough draft is more than half finished. I have at least four more chapters to write, and then I will expand on every chapter, before I begin the editing. I believe I will be putting lots of my personal graphics throughout also instead of using an illustrator.
My third book, which I expect will be published in 2020, is a children's Christmas picture book titled Christmas is Coming. The busy, rollicking "North Pole" story is differentiated completely from Merry Tilda, A Winter Fairy Tale, my first holiday story.
Of course, like every writer, I have other books either in the works or in my mind. If you are a writer ready to think about publishing, I suggest you build a repertoire of at least six finished pieces and another six "possibilities." While you are preparing these, you can be looking at your publishing options just to put a little variety and anxiety in your life!
I'm not expert on publishing, nor on marketing, even though I am learning in both areas. I suggest you explore those areas since you will need them. I am an expert on writing and will gladly share that expertise with you. It settles out to this: You must love to write, you must write often, and you must be happy (or willing) to edit and revise your work even more than you actually write. And, of course, you must read. That's it. That's my very knowledgeable bottom line. Bet you're already doing those things, aren't you?
Yes, there is more to say ... one of these days. But if you follow my wisest advice above, you are already in the game. Good luck, writer. Good work ahead.