Drawing backgrounds

For some time, I've been trying to figure out how to draw backgrounds with detail, but at the same time, make them quick and easy to draw. 

There's a technique that I noticed in some cartoons where detailed backgrounds are painted with an "imperfect" sort of feel to it. The lines are mostly loose. The colours focus more in lighting & shadows, sometimes not even in line with the lineart. The main subjects are drawn normally with minimal shading and details. See what I mean, here. 

I kind of took some inspiration from that. I found that painting areas where there would be a lot of detail was a lot quicker and efficient than drawing every detail in the picture. I also found that painting with a more transparent brush that mimics how pain works in real life was quicker than cel shading because I could be looser and more laid-back.