This photo is pretty simple, light on the bottom, dark on top. Two of the figures are in sunlight and the others are in shadow. Still, it could benefit from making that light/dark structure more obvious. I'd like to exaggerate the brightness of the two closest figures. The one on the left could have lighter pants, for example, and the guy behind him could have sunlight on his hat. What about the graffiti? It's just a bit too distracting. Should it be eliminated, or just turned down a little? While we're at it, maybe the doorframe should be a little darker.
The idea is to make it easier for the viewer to get your message. If you want to display the difference between the sunlit and shaded areas, consider making adjustments that clarify that relationship. Of course, this presupposes that your main purpose is clear to you in the first place.
In the market scene, above, the figures that are near us are quite different from those way in the background, but they are not so clearly separated from the middle-ground shapes. I am inclined to make the three closest women (and their baskets) more similar to each other and less like the five or six people just beyond them. How can I use edge quality, color, value and composition to make the space easier to read?
Look for a way to group the buildings into three separate levels of depth. That patch of sunlight could help, as could making the most distant buildings into a single shape (look again at the domes and towers in the background of Zbukvic"s painting).
Pick one of these photos, or use one of your own to practice simplifying by grouping adjacent shapes and adjusting color, value and edges to make them more similar.