I’m a fan of ABC stories (or ABC flash fictions). How it works: starting with A, each sentence begins with the next letter of the alphabet. You could also start on a different letter and run through the alphabet like a loop (start at K and end on J) or start at Z and go backwards. This won’t get you all 1667 words for the day, but it’s surprising how creative you can be when there are limits to what you’re allowed to do.
If you haven’t done much planning, you can also use this exercise to create a quick summary at the beginning of your story