I began with a story fragment of 154 words and have written for a week, holding myself to at least two hundred words per day. Now the story is at 2,200 words. The good news, though, is that as I've been writing, the words written each day have grown, the last two or three days much more effortless and sustained.
I even missed one day of writing when I had an early doctor's check-up and other commitments, but I was already a little ahead of schedule, and the next day wrote more and caught up to my scheduled words.
The most engaging experiences have been those moments where I begin following a thread of plot possibility that I hadn't thought of until I began writing. Then I'm off into new territory, and it's quite fascinating witnessing myself write down the progressions and open in my mind. My experience is that this becomes more possible when the daily flow of words is established by routine.
That's the process, though, the first draft opening all the doors and windows. Or as e.e. cummings described the "spring" season experience: mud-luscious. Can't you just feel the mud squeezing up between your toes as you make your way down the path to the river?