Here's a day's work on my zoo painting. I begin by transferring the finished drawing to Rives paper using graphite paper. Then I mask the edges with one inch painter's tape. Next I lay down a thin wash of burnt sienna. I have a tendency to work really brightly, so this wash helps tone everything down a little and make it look a little more realistic.
I block in the backgrounds. I'll probably go back to add details to the sky and ground later on depending on how it looks against the finished figures.
Working background to foreground I paint the giraffes. Shadows and highlights are done first and then the detail of the spots is painted on top.
I add some fine light blue linear work around the heads to pop them forward. Out of curiosity, and needing a break from the earth tones, I block in the sunglasses, hair, rocket pop and dress. I'll probably need to redefine these once I get the flesh tones on, since I'll probably end up painting over the edges.. which is why I usually try to work background to foreground. It saves a lot of time on touch ups in the end. Sometimes I just can't resist breaking away and working on a part of the painting that seems more appealing.