Writers often use prompts and time limits to warm-up or unblock. I do much the same thing when I draw. I give myself a time limit. Usually 30 minutes. Then I pick a short story that I have already read, re-read a page or two, and illustrate what I've read. Roughly. Very roughly. I like to use panels, and I like to make the narrative part of each panel.
I rarely illustrate an entire story, but I do use a separate panel for each individual thought without skipping around or editing the text, even if I've chosen only a page or two.
The time limit keeps the sketches as ideas as opposed to artwork. Depicting ideas pictorially without the constraints of correct technique or finishing touches keeps the work clean and abstract. Mistakes are not considered mistakes. They are part of the exercise and stay put (note the two m's in Hemingway).
It's easier to move on to more sophisticated work when you begin with something clean and clear that helps you see instantly what to keep, what to add or replace, and what to throw away.
It's like warming up at the piano before a concert. My daughter plays, and she often warms up with the Goldberg Variations (see video below), playing them excruciatingly slowly at first, no matter how many times she has played them before. For me, this is similar to a piano warm-up, except that I keep it simple and quick by limiting my time and choices.
This type of illustration is sometimes later finished, then published as artwork. Take a look at The Graphic Canon, Vol. 2: From "Kubla Khan" to the Bronte Sisters to The Picture of Dorian Gray. If you click the link, you can view a sample of the book and perhaps have a clearer picture of what I'm talking about.