Let me amplify some of these a little.
Once the facts of the subject of the narrative are known, we have to decide upon which passage of text we are to illustrate. 
We then ask ourselves which idea shall we take up - and which compositional and drawing approach will best serve the idea.
The question ‘when’ involves thinking about when to stop the action of the possible scene to be depicted and choosing the precise moment when an event has just happened, or is about to happen, and that will, or may, in the next moment change. 
The expression in the drawing has to be as forcible as the subject may appear to be instantaneously fleeting. 
For this illustration, for my own story of The Giant Jam Sandwich, I chose an important moment, showing how a slice of bread from the giant loaf was cut.