Let the idea ferment for a while (six to twelve months is about right).
Eventually decide that the idea has been brewing for long enough and decide to write it.
Stare at an empty page (Normally for another six to twelve months).
Set yourself a deadline (for about twelve months in the future).
Attempt to hit deadline.
Stare at blank page a little more.
Manage to slide into your deadline like a baseball player skidding in to fourth base.
Sometimes the words come easily. At other times, inspiration just refuses to come and play. Sometimes finishing a book can seem like a walk in the park. At other times, it may take years before your beautiful idea is finally finished.
Other than blood, sweat, and tears how do you write a book? Do you start at the beginning? Or plan the ending first? There are many tried and tested methods out there but, at the end of the day, it's whatever you feel comfortable with. You may find that the ideas flow easier when you're sitting in a certain spot or writing a particular scene. If that's the case, do it. Write random scenes and then link them together. Much like a jigsaw, you're creating a bigger picture from lots of tiny pieces. The story you tell is a subway of interconnecting stories and ideas.
Your idea is one of the most important parts of writing. Love it, cherish it, nurture it. Pick up a notebook and make notes. Keep ideas of scenes and plot points. Create flow charts of how the story will run. Index cards are fantastic for noting down ideas and allow you to move them around at will.
Books can seem like complex characters and, to a degree, they are. They take hard work and dedication. But you can break them down in to much simpler steps until you have the finished product in your hands. Grab a pen and paper, sit down, and start. It's that easy!