Outlining and passion help. So does having nothing else to do. I've typed about 20 pages in the last 24 hours (written a bit more). For me, that's a lot.
I find it helps to write a section in another time or place and then rewrite it on my computer and not really look at what I wrote earlier. The writing the first time is just to get the dialogue and action down, so I don't forget the idea. When I get to my computer, the idea has had time to evolve and imprint itself in my brain. The bit that I wrote earlier almost always changes.
I'm a little over halfway done with the spec pilot for this drama miniseries I'm writing, and I know the exact story arcs for two parts, sort of the story arcs for two more parts, and am still outlining the fifth. It's actually really really exciting. I hope someday it gets made. It's going to have four acts (maybe five) and a teaser and probably six episodes. One for before the event (about 4 years), one for the beginning, two for the event, one for the end of the event, and one for an aftermath sort of thing (maybe to bookend, another 4 years after, not sure). Maybe only five episodes. I haven't really broken it down. But let me tell you - it will be great TV.