Joan Acocella, in a review of Richard Greene’s (no relation) The Unquiet Englishman, describing Graham Greene’s writing routine:
Graham Greene was an almost eerily disciplined writer. He could write in the middle of wars, the Mau Mau uprising, you name it. And he wrote, quite strictly, five hundred words per day, in a little notebook he kept in his chest pocket. He counted the words, and at five hundred he stopped, even, his biographer says, in the middle of a sentence. Then he started again the next morning.
I like this. It’s simple and can be done anywhere.