I have read many books of many different genres. Most of them I wanted to read on my own will, but some of them were assignments from school. Most of all the books I read were fascinating, most of the time. In my eyes, the important thing about writing a book is having a lot of ideas.
My favorite genre has always been Fantasy/Sci-Fi books, the big, thick kind of books that take a while to read. There is a simple reason for this: In a fantasy world there are no limits and you can write about your whole imagination in a new environment. I really respect people who use the real world in a book and no science-fiction at all. I know two real, really successful fantasy writers, and I would do it the same way they did it.
I would start off with creating a cool map of my own invented world, like all the famous fantasy books. After that step I would think of some main characters with fancy names and then I would start writing.