Step 1) Writing a book is a marathon, not a sprint. You may have days when your Muse is flowing through your body and your thoughts--you will have days when coffee becomes your artificial inspiration. The first step in writing a book in 1 year is taking the time out to write 1 page a day everyday of the week. By the end of the end of the year, at this rate, you'll have a 300 page book. Don't just write when you "feel like it."
Step 2) The second step in writing a book in 1 year is figuring out what you want to write about. Do you want to write about a lonesome couple who finally gets that pet labrador or do you want to write about the murder of a Benedictine monk? Knowing your story is crucial.
Step 3) The third step in writing a book in 1 year is to organize your plot. Outlines are helpful to many--my outlines are loose since they typically constrain my writing flow. Whatever works for you regarding outlines is ok. I hope this has been a helpful article on how to write a book in 1 year. Good luck!