Birth of the First Rambo

Because I am a very amateur writer, I am attempting to write a book-sort-of-thing, but this is my very first attempt at anything more than a short story, so it may not be very continuous (as I am used to writing simple essays or stories). Tell me what I can do to make it more professional, for I do not know much about being an author. I want to edit it and evolve it into something decent!