Gather your materials. Get your basic idea, your outline, your research, corresponding documents, and any other material that you need to reference.
Set up your work space. This can be any place where you get inspired. A dedicated desk or table, a desktop computer or laptop with a word processor can be helpful. You'll need a paper and pen for notes, and don't forget a dictionary.
Decide what type of book best fits your idea and your material. If you are writing a how-to manual, your style will be much different than writing a novel inspired by your own experiences.
Set your focus. Narrow your topic to something appropriate that you can write about with clarity in the time you have.
Make a rough estimate of the number of pages required for your book. Divide the number by 14. That is your magic number. Produce that number of pages every day, and you will have a book. If you can write more than the set number of pages in a day, that's fantastic. That means you take it easy on another day.
Set your schedule. Do your best to clear your schedule of activities, social obligations, appointments, meetings, and other projects. You have to focus on this book. Put a vacation responder to work on your email. Change your voice mail to let people know you are busy and will respond in two weeks. Make a grocery trip and get prepared food so you won't need to spend time cooking. Decide on a starting time (early in the morning is usually best) for each day and write it in your calendar. You'll need to take breaks, of course, and you can go ahead and put those in. But don't stop writing for the day until you get your page quota written.
Let people know. Tell your family and friends about your project. Most of them will think you are crazy, but they'll be secretly jealous at your drive, determination and the amazing sense of accomplishment you will have at the end of it.
Write! Every day, for 14 days, no matter what. Stick to your schedule. Take periodic breaks to refresh yourself. Walk around the block a few times every day. Drink lots of water. When you've completed your pages for the day, try to get outside and do something active to give your brain a chance to unwind and your muscles a chance to fight writing atrophy.