Today I had the opportunity to listen to Peggy Thomas, the author of Farmer George Plants a Nation and Thomas Jefferson Grows a Nation.  She gave some pointers on how authors publish their books.  The first suggestion she gave was to polish your craft of writing.  Joining http://www.scbwi.org is one way to work on writing skills.  Another suggestion was to publish magazine articles such as in Highlights, Spider, and Cricket. https://www.highlights.com/contributor-guidelines