I sketch it out, then I write till it's done. I aim for a min 500 words a day, a chapter a week but - considering my current wip is almost 2 years in the writing and currently 95,000 words long, I'm probably not the person to advise you. Honestly, the notion of writing a fic in a week is an alien concept to me. *g* But that's probably not a good thing. :o)