Sometimes we have to trick ourselves into writing. The desire may be there and the deadline fast approaching, but we're simply too tired or distracted to focus on composing.
That's when listing may come to the rescue. Jotting down a few stray thoughts or images can be done on the sly even when we're not in a writing frame of mind.
It's a trick that E.B. White occasionally practiced when drafting short pieces for The New Yorker magazine. Here's an early example (later reprinted under the title "Unwritten"):
Sometimes we regret our failure to write about things that really interest us. The reason we fail is probably that to write about them would prove embarrassing. The things that interested us during the past week, for example, and that we were unable or unwilling to write about (things that stand out clear as pictures in our head) were: the look in the eye of a man whose overcoat, with velvet collar, was held together by a bit of string; the appearance of an office after the building had shut down for the night, and the obvious futility of the litter; the head and shoulders of a woman in a lighted window, combing her hair with infinite care, making it smooth and neat so that it would attract someone who would want to muss it up; Osgood Perkins in love with Lillian Gish; a man on a bicycle on Fifth Avenue; a short eulogy of John James Audubon, who spent his life loafing around, painting birds; an entry in Art Young's diary, about a sick farmer who didn't know what was the matter with himself but thought it was probably biliousness; and the sudden impulse that we had (and very nearly gratified) to upend a large desk for the satisfaction of seeing everything on it slide off slowly onto the floor.
(The New Yorker, April 26, 1930)
Next time you find yourself stuck on a writing project, call to mind some things that recently interested you--things you have been "unable or unwilling to write about" but that "stand out clear as pictures" in your head. Then start listing those things. Briefly describe or explain them one by one without regard for coherence or consistency.
Perhaps, like White in this example, you'll wind up with little more than a series of random observations. But you never know. One of the items in your list may trigger a deeper response. And at that point you may decide to abandon the list and focus on developing a single image or idea.
In other words, you might fall for your own trick and find yourself in a writing frame of mind.