via Negative Spaces
Interaction is not the only element that makes two figures better than one in a picture. There is a more graphic aspect.
In abstract terms, a big reason two figures make a potential picture is that there is interesting negative space between and around them.
Even simply filling these shapes with flat colour like this causes the figures to stand out and reinforces their connection with each other.
This is a simple, basic way to develop a picture from a drawing without losing any of the drawn quality. It brings integration and clarity, two key aspects of composition.
In each of these examples I have halted the background at the point where a floor might begin. This gives the impression of a different dimension: a horizontal plane. It doesn’t have to be a horizontal dividing line, of course. A diagonal, even a mild one, would be more dynamic:
The important thing is that the qualities of the drawing have not been diminished in this process. This seems to me to work a treat where the drawing is as assertive and lively as Maria’s (above)
Adding a simple flat colour (below) turns this drawing into a classy illustration with a feel of the 1950s, an era when publishers could often only afford to print one extra colour besides black.
I stress tackling background first because it holds the subject together, and once it is in place it is then so much easier to select and place colours for details in the foreground:
The more graphic the drawing style, of course, the easier it is to use graphic techniques (of the sort you find in Photoshop) to colour the rest of the picture.
Indeed, taking this approach can sometimes make a strong picture out of the loosest sketch…
…so that the looseness becomes enhanced without losing any liveliness.