I thought today I would show some of the background art that I did for "Cartoon Network: TKO." I can't seem to find my sketches on these (darn organization) but I am able to show a "set up" version of the scene, and then a blown up view of each layer. The set ups are not quite final, but the layers that you see in the cut-away versions are what made it into the game.
In the final layers, I added a few signs of life. Laundry on the line, some extra business signs, and a few antennae.As you will notice, simplicity was key. Some of my first ideas were over complicated, and fought with the characters for screen time. I think these simpler, softer approaches really helped the robots pop off screen and allowed the player to focus on what they were supposed to.
So, in a nutshell... simple soft backgrounds with minimal detail allow your characters to pop.