Barry L. Hughes
When I get an idea for a script or a book it either comes to life or it doesn't.
I do a lot of mental story outlining. If it gets past that stage then I will put it on paper/word processor in the form of a short one-paragraph logline or mini-synopsis.
If it's still alive after I put it on paper I then begin a file I call "Outline" where I begin writing ideas for the different aspects of the full story including main characters, etc.
If I'm still interested, then I'll begin writing the ending first and then try to figure out how it should begin.
With The B&L Show there was no hesitation. All 423k+ words were written start to finish in almost exactly a year. That included edits and publishing the first (very rough) edition. I felt like it became as much an obsession and divine inspiration as anything. The final book was written in one month and the final chapter and Postscript in a single day.
I think the final book was so quick because of my outlining process. See my answer on writer's block for more.