By coincidence, Donna, Dean, and I are all at the same point. I, too, am about to start a new book. Furthermore, it'll be the first in a new series. As many times as I've started new books, this procedure ought to be stress-free; but it's not. The only comfort I have is that I can't make any continuity errors, since there's no previous body of work to coordinate.
This time, I'm starting by drawing a map. That's so much fun it ought to be against the law. I love creating a new town, and I already have a good idea of most of the people who live there. After I draw the map, I'm going to refer to the book synopsis I had to create when my agent was selling the book. Since my editor and I have worked together a long time, I know it's not necessary to stick to that slavishly, but it's a definite guideline.
Then I have to decide at what point in that story the book will open, which will determine how much backstory I have to insert.
And finally, I'll type "Page One, Chapter One" and the first sentence will flow. After I set the tone and vocabulary for the book, I may rewrite the first sentence several times. Next July, I'll write "The End."
That's the plan, but the experience of writing every single book is different. And it doesn't get any easier! I still can't imagine doing anything else.