I start laying shadows with multiply and start working some of the lighting in the background. I tend to go opposite on my shadow tones to make it more dynamic, meaning if I have warm basic tones I like cold tones for the shadows.

 
 
 
 
 
Then I start laying some of the lights on the characters by adding a layer on top of my shadow tones and base tones.

As a final stage I tend to go over the whole image and clean up any missing lines from the original drawing, do some color corrections and add a couple effects.

 
 
 
 
 
 
 
 
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