The above is a sketch I did for my upcoming picture book, As Yet Untitled Wildly Successful Pig Vehicle. It depicts the untitular pig reading upside-down atop a statue of a proletarian accountant (it makes sense in context) (sort of).
Keen viewers will notice the building behind the statue's left arm has been left unfinished. And with good reason: I gave up on it. Why? Because this drawing is what we refer to in the illustration business as "irredeemably bad."
Here's the same scene again, with the bad removed:
So what's the difference? Why is the bottom illustration more engaging that the top?
Lots of reasons: cooler-looking buildings, the first statue has that dumb tie, etc. But the most important reason, especially for a picture book, is that the original illustration has no obvious subject. The statue, pig, and buildings are all vying for the viewers' attention. So what was needed was a better composition to direct the eyes to the subject of the illustration.
Creating a composition with a clear subject can be done using color (putting a warm-colored subject on a cool-colored background, or vice versa), tone (putting a dark subject on a light background, or vice versa), by arranging the elements of the piece to frame or point to the subject, or some combination of the three.
Subtle artists will nuance the image elements so the viewers won't even know they're being guided. On the other hand, I basically made the statue into a giant arrow pointing at the pig.
And in case you didn't get it, the building below the pig also points in his direction. Nearly every element points towards the tiny pig. LOOK AT THE PIG, GUYS.
Of course, there's many examples of great illustrations that straight-up flaunt compositional clarity and still end up looking dope. But this is how I work. And this is why I work slo-o-owly.