Here's the gif showing the process in which i paint backgrounds.
I paint from the back to the foreground. But generally it is sketch -> base colors -> and then refine, refine and refine.
It will help painting if you have already established the values and the colors you want to use. For this reference photos with colors you like would help.
Here's the clip file for those who want to see the layering.
And that's all. Thanks as always!