Here’s an exercise that doesn’t guarantee quality prose (or 14 lines of rhymed iambic pentameter if that’s your hankering), but it does guarantee ink will hit the page.
From Julia Cameron’s The Artist’s Way (p. 10):
Put simply, the morning pages are three pages of longhand writing, strictly stream-of-consciousness…[Morning] pages are meant to be, simply, the act of moving the hand across the page and writing down whatever comes to mind. Nothing is too petty, too silly, too stupid, or too weird to be included.
I try to perform this drill daily, but in practice I do it about five mornings a week. Sometimes I just babble endlessly about minutia (like how I need to get a new toothbrush), but other times I end up with material that I can use elsewhere (see blog entry, this one).
If nothing else, writing morning pages is a great way to clear your head before starting your day.
Also, I used to type mine, but found the exercise to be more meaningful by following Cameron’s suggestion to write longhand. (As I’ve mentioned earlier, I use a Moleskine large ruled notebook and a Fisher Chrome Bullet Space Pen—both of which I recommend.)