(Posted on quora for the question asking about the writing process of authors)
I will just add my writing process and experience to the many answers below. When I went through these answers, many were surprisingly similar to what I do and I guess what many writers do. Not very surprising though, this is diametrically opposite to what most people perceive what writers do.
Writers have many ideas that keep popping in their head based on their interactions with the world and their own thoughts about the past. Sometimes, one of these ideas becomes strong enough to be put on a paper. Most writers have many such ideas documented in their journals, their writing software or simple editors. Several writers try to capture such ideas everywhere. They carry their journals everywhere in their pockets and note those ideas. Some do it on their phones. This is very well captured in some movies about writers, like Patterson.
(Patterson writing a poem before he starts on his day job of a bus driver)
Most of the writers, like I do, have a writing routine. I wake up every day at 5am and sit in front of my computer with all the ideas that are captured in the writing software. Unless I am working on a novel that needs to be completed with a deadline, I write on multiple projects at the same time. You start with one of your many ideas, the idea that really motivates you to write on that particular day and crank at the keyboard for next couple of hours with small tea break.
In dues time, if you are persistent enough, you will write many, many words, paragraphs, pages and eventually a book.
I hope that explains the process of writing.