Of course, it starts with an idea. My first eight books were somewhat easy in the sense that I knew exactly what I wanted to write. So, if you do, fantastic. Right now, I am contemplating about my next book. In fact, I sat with my publisher last night about it. We discussed the potential covers for Snow Blood Season 5 and Kane's Story. Afterward, since Season 5 is the last of the Snow Blood Series, we kicked around starting a series about Kane and pulling a character (a canine of course) just briefly introduced in Season 5 to tell his story. My point is, that no matter whether you know exactly what you want to write or not, it's a good idea to bounce your ideas around with either avid readers of your potential genre or a professional writer or editor, if you know one. Worst case scenario, just talk to your best friend about it and see what he/she thinks of the idea in your head. You should try to gather some enthusiasm for your project.
Next, whether fiction or non-fiction, create an outline. I like to make each point in my outline represent a chapter. By outline, I don't mean a one or two word description. Let er rip! Put down all your ideas for each chapter. I have great editors and a publisher to look at mine and give me feedback. Again, someone interested in your potential book could be the person to bounce ideas.
Then, once your outline (I think of it as a road map) is completed and ready, start writing at chapter one. and go through the story sequentially. Do I move things around and have additional ideas as I write? Absolutely. That's the fun of it. You don't have to completely stick to the outline. Again, it's just a road map to keep you on track.
Write a little every day. Try to commit to an hour minimum. Otherwise, you'll never get it done. Don't worry about making it perfect, just get the story down. (As a writer, I write all day long, but I have clients and marketing and... well, you know, life that take up a substantial part of my time.)
Once you have a rough draft, go back through and tweak it as many times as it takes for you to be satisfied.
Then, get an editor to work with you on content and proofreading/line editing.
Take the editor's suggestions to heart. It may take several rounds of editing with a professional to perfect it.
Once you go through this process, you'll have a completed manuscript. You'll be ready to see if you can get it published, but that's another story!
Til Next Time,