Here we see Mr Mead having a mainly blue-coloured nightmare in his garden.    
‘What’ is a question of identifying the various components, objects or props (such as clothes and furniture et cetera) that may be included in a picture, as well as deciding about those that may be omitted. 
There is also an attempt to reflect, in the drawing, the tone of the narrative - by extracting the sense of the mood and atmosphere of its content.
The season, the weather, and time of day or night, might be an important consideration too.
Compositional devices and physical marks in drawing naturally have a contributory bearing on how atmosphere can be conveyed.
What – is also a question of what you want to evoke in your illustrations - something that is unique or different from others.
One of our main quests as illustrators is to try and be original.