Step 1. Make microwave popcorn in your microwave oven.
Step 2. Rush to your computer/notepad/whatever and write as many words as you can before the bell dings.
Step 3. Eat some popcorn and read a book.
My popcorn takes two minutes to cook, and I managed about 200 words in that time. It was surprisingly motivating: forcing myself to discard all internal squabbles and doubts in the name of sheer productivity.
And for only a minute and fifty eight seconds!
I've already moved this strategy into the general realm of my writing style. Got five minutes? Write. Got a minute? Write. And then: got an hour? Write for half of it, and play videogames the rest.
Overall, I'm actually more productive, happier, and having more fun when I'm writing this way than when I was pounding out the longer sessions. I... can't really say why this is. Especially since I'll still go for the long haul if my fingers tell me, "Yeah, alright, this is pretty cool;" but if not, I'll just whip them up to another frenzy in another ten minutes, alright?
Now, for some popcorn.