(w) Brian Azzarello
(a) Cliff Chiang
(c) Matthew Wilson (me)
Here's an example of how textures and details can really enhance the setting of a scene. This clinic is in a lower income area of a pretty poor state (that info is from the script, btw). So, having grown up in a very similar area I remember many offices being lined with cheap wood paneling that had a prominent fake wood texture. These offices also had carpet that was 20 or 30 years old, and a horrible color that would never be used today.
I took the one line from the script, and in this case used personal memories and applied them to coloring this location. You can conduct internet research in cases where you don't have personal experience. But one way or another try and give the setting life by finding out details. The backgrounds are essentially another character, so make sure to treat them like one.