1. Finding the Time
A book is a mammoth effort - usually 60,000 to 100,000 words. Of course, if you participate in Nanowrimo during November and manage to reach the 50,000 word goal, you could, in theory, knock off a good chunk of your first draft in thirty quick days.
However, if you're a busy person with a job and a life, with friends and children and parents and umpteen commitments to meet every day, then reaching a target like this might not be possible. Stephen King, a writer who I greatly admire, says, in his biography "On Writing", that he writes every single day of his life. Which is all very well for Stephen King, because that's all he does. I know that's not all I do, and I bet it's not all you do, either.
I have found a better solution to be something like this: