Jane Yolen, one of my favorite writers, and people, too, muses about her writing rhythm:
". . . on the good days, what is it that makes me more fluent, more creative, more on game? I know for me that light is a key . . . Priming the pump helps--doing email, galleys, revisions, the journal. And if I am in the middle of a large project and it is going well (novel, long short story, the final editing of a poetry book) the momentum simply sustains itself."
Observe your energy highs and lows. What feeds your energy? What saps it? When you understand your rhythm, you can give yourself grace and understanding for less productive times. And you can flow with the energy when it's there to help you, even if your schedule seems arbitrary or odd to outsiders.