How to write a book
Buy a notebook. Or several. While you may wish to type your novel directly into a computer, it's not always possible to be near one when inspiration strikes. Thus, it's best to have good old-fashioned pencil and paper no matter where you are. Moreover, many writers swear by the connection from mind to hand to pen on paper, so at least give it a go before dismissing this as an option to aid your writing experience.
A leather-bound or heavy card notebook is the sturdiest and can take lots of abuse in a backpack or briefcase, whereas a spiral-bound notebook, while not as robust, is easy to keep open. Better still, should you decide the page you just wrote is utter garbage—it's easy to rip out!
Spiral or bound, consider using graph paper versus standard lined paper. You may end up creating drawings and sketches as you go, and it's useful for indenting paragraphs, or outlining.
Put your thinking cap on. Now that you have your notebook, it's time to squash the traditional bugaboo of all writers: that empty first page. Use those first pages to create the overview of your story including an outline, notes about characters (possible names, descriptions, "back stories", etc.), places, era—all the little things that go into a larger story. There are several advantages to this overview approach, including:
It will give you new ideas for your story as you describe different parts of it (write those down!)
Nothing goes to waste. You may describe a character, for instance, who never appears in the story directly but who influences another character.
You always have something to refer to when you run out of immediate ideas.
Create your outline. An outline will help you define the arc of your narrative—the beginning, development of plot and characters, the setting up of all the events leading to the big conflict or climax, and then the resolution and ending.
The beginning of the story is often the hardest part—if you want it to be. The best thing to do is start as broadly as possible. Say, for example, you want to write a mystery novel, and you're a fan of World War II. Write that down: Mystery, WWII. The beauty of this is that both categories are very broad, but simply by putting them together, you instantly narrow the field of possibilities. You now have, at the very least, a time period, and a focus. Something mysterious happened during WWII. Try to focus it a little more.
Is it personal, or is it sweeping? WWII was certainly both. For the sake of example, say its personal, one soldier's story.
When does it take place? WWII is obvious if it's about a WWII soldier's story—or is it? This is one of those decision points you will come to right away. Say it actually takes place now, which leads to the next question, "How now?” To move right along, lay out the beginning scenario: Your main character finds a journal—his grandfather's journal from WWII. This is a revelation, because Grandpa never made it home from the war, but nobody knows what happened. Perhaps, in this journal, your hero will uncover the answer.
You now have several key questions answered, right out of the gate: who: your hero; when: then and now; what: a journal, and the mystery of a missing person. You don't know "why," yet. That is one of the things you must discover. How? Again, this must be uncovered through asking yourself questions.
Develop your characters. Start with the obvious. In this case, you have already created two characters—a young man and his grandfather. You can determine characteristics of both simply by the setting, and expand your characters in the process. Grandfather would likely have been married, so there would be a grandmother in the picture. There's a generation between grandpa and the young man, so there would be one of his parents who is also Grandpa's son or daughter. See how easy that is?
Continue along in this fashion, extending from one character to all the others that they may interact with. Before long, it's possible that you'll have too many characters and interactions. This is good, especially in a mystery. You may have need of "red shirts," like the hapless, disposable ensigns from the original Star Trek!
In the process of developing your characters, you will likely ask yourself the same question your readers will soon be asking: what happens next? Use these questions to develop the story. You know, for your story that the young man wants to find out what happened to Grandpa. Since all he has is the journal to go on, he reads it, and discovers Grandpa's story that lead him from his small town in Kentucky and his pregnant wife (grandma!), to the beaches of Normandy, to finding himself wounded behind enemy lines—all of which he wrote of in his journal. He never makes it home. Knowing these things, you see questions and a pattern emerge:
Events take place in "today" time, and also during WWII: As the journal is read, the date is 1944. As the grandson explores, it's today.
To add some action to the mystery, the young man must do something. Since Grandpa isn't coming home, send the young man to Germany to find him—dead or alive.
Where was Grandma in all this?
Continue along this process of creating the arc, but at this point you could even hazard a tentative ending: the young man discovers why Grandpa never made it home, and how his journal did. Then all you need to do is write down everything in the middle!
"Timeline" your outline. Now that you've created the basic story (minus all the words), sketch your outline as a timeline, with each character's milestone events laid out on their own line. There will be times when two or more characters intersect, and where some disappear altogether. Just draw a line where those events happen. This too will give you something to kick start your muse when she falters.
Edit mercilessly. If you find your plot goes nowhere, and nothing you can do will help it—back up to where it last made sense, and try something else. Your story is not required to do anything you tell it to do in the outline. Sometimes, the story has other ideas where it wants to go. Wherever you are in the process, the muse may beckon you elsewhere. Follow her—this is part of the joy of writing.
Write your novel. With your story and characters prepared, you know what happens next: tell the reader how the hero got from page one to page 500!