Decide what kind of book that you would like to write and read other authors in that same genre. Jot down a few notes about each story in a notebook. Specifically state what you liked about the story and note what you would change about it. Put your notes in a place where you can refer to them often.
Find a writer's group online or in your hometown to join. Attend weekly or monthly meetings and network with other members. See what kinds of ideas other authors are working on and pay attention to any advice they might give. Many published writers seek the support of other people in their field for camaraderie and mentoring despite having a book for sale in the marketplace.
Attend workshops, writer's camps and classes either online or in person. Use the opportunity to embrace your creative side. Try writing the same story or poem in a variety of ways.
Make it a point to write for several hours each and every day. Find your own quiet place to do this and free yourself from anything that you might find distracting. Set a specific goal for your writing and try to exceed it.
Once you have completed your manuscript, search the web or gather contact information for publishing companies from books and magazines. Draft a cover letter introducing yourself and your story to the editor and enclose it with your completed novel or memoir. Send it to the contact person whose name appears on the list.