How to write a book

So I have been working on stories, long and short, some hoping to someday make it into a full-blown novel. I have been writing, fairly inconsistently, but putting words to paper none the less. There comes a point when you start second guessing yourself while you are putting together a story, and wonder if this is the right story for you to be writing. What I mean is, is the material, the subject, the world you are trying to create may not be one you have the personality or knowledge to write well. I am currently trying to write a Noir novel, a novel with murder, betrayal, and no clear delineation between good and evil. I know the genre, but I am no expert. I question if my limited experience in this type of story is going to be enough to provide me with enough to write, and whether any of it will be any good.

I guess any writer probably doubts themselves, even John Irving had to wonder if anyone would like his books. Some people say that you should write what you know; that your life experience will provide you with the best stories. Others might say that as long as your creative juices can cook it up, write it. The biggest test is whether or not people will read it and appreciate it, and enjoy the stories you tell. Maybe I am being a bit ambitions with a Noir novel, but it is a fun genre and alot of fun to write. Maybe I should write what I know, write from the experiences of my life; I know I have plenty of those stories to tell.