There are several actions, details and emotions within a written scene but an illustration only needs one moment, one visual. Let us assume a written passage in which a child walks into a kitchen, he observes an open window, he notices mud footprints and he hears a cupboard door slightly open. This would mean that four things to draw and they might result in a composition with no clear focus. A much better choice could be the moment of the child spotting the footprints and the resulting surprise since that moment can include action, emotion and a mystery the reader wants to know more about.
The first task is to condense the writing into a single sentence of the most significant visual action in the scene. Not to describe the story, but to describe the one thing that the reader must know in this scene: “A child has found mud footprints leading to the cupboard.” This includes a character, the action, the direction and the focus. This also helps to separate important story beats and the less important ones that do not have to appear in the illustration, but may stay in the manuscript.
The next step is to look for story beats with the most visible change. A character may enter a room, feeling content, and suddenly they are surprised. They may be about to take a cup but not take it after all. They may walk into a safe room and feel uneasy. These transitions are a lot easier to portray than static moments since you can show the action with gesture, pose, framing and facial expression. It is often also the moment before or the moment after an action that is a bit more interesting than the action. A child with a hand slightly raised as he is about to take off the cupboard door is probably going to be more exciting than showing a child that has already taken off the cupboard door.
When it is finally time to sketch your composition, you can create several thumbnails to get a rough idea of the final illustration. Make the drawings tiny, so that you don’t end up adding detail to them. Try for a composition where the kid is close to the viewer and the footprints lead off into the background. For instance, try looking from inside the cupboard and you will see what the child would be facing in front of him. You may also choose to show the entire room, with footprints leading into the background across the page and the child in a small corner. This comparison may give you an idea of which camera angle works best, with the clearest focus point and strongest design.
You may then look at your sketches by looking at them in silhouette. Make a dark area, with small details, colors, texture and line weight being ignored. Is the content still clearly recognizable? Is the direction of the character or a hand gesture obvious? Is the direction the reader’s eye goes from the character to the clue? The silhouette may reveal some mistakes or changes, and if the pose is not readable without facial expression or line work, you should try adjusting it. You can achieve a very clear expression of surprise with a slanted torso, a stopped stride or arms held out from the body.
The last step is to make sure the scene will work with a text area. If it is a double-page spread, it is important to create negative space on the page where a text may fit into, or you may hide parts that are too close to the gutter. The background should set a scene, but should not compete with the character or action. If there is a table, a window and a chair that sets the scene, then you may not need every jar, plate or floor tile that is in high contrast. You may use scale and value to emphasize the main action.
The last step is to ask yourself how you may describe your rough illustration without using the written story. A child stopped after seeing a trail that goes somewhere else, will be enough if the picture shows a clear moment, and if it is more difficult and you have to talk about lots of different things, you may have to change the focus to a single part of the manuscript. Choosing the right scene doesn’t mean showing everything the writer wrote, just giving the reader one illustration that will make the other elements stand out more.