Attached Link: Sketch

I have made a preliminary sketch (link above). Now I want to make it into a watercolour painting. Not by any automatic process or filter, but by carefully handcrfting each layer. I am looking for any advice that my be helpful in that process.

I know that there are a lot of tutorials out there for instance at Good-Tutorials, but there are too many.. some are several years old. Surly by now some kind of best practice has envolved?