I don't know if this is how one is 'supposed' to work through these sorts of pictures, but really it's art and there is no one right workflow, just whatever works best for you is what your roll with.
You've probably seen quite a few of these sketches, sometimes I post them just like this. Really this is the first phase of me getting into a drawing.
http://i.imgur.com/fBsJ6ai.png
The next step is to add outlines on another layer. I know some people think you should paint and really try to work it without black outlines, but I honestly like them "It's part of my style" is often cited as a lame excuse by mediocre artists to get away with whatever they want, but I really do like the graphical style of the black outlines, particularly since my style is to not go full realism. (Except in some of my graphite drawings from my class which I will really have to post at some point.) Though in this style, would like to start practicing variation of line weight and such.
http://i.imgur.com/8xD3ZtF.png
Now this, this is what usually eats up the bulk of my time, coloring and shading. It's generally just work getting the colors to go inside the outlines, then adding tints and shades around a character to add depth and shine. Like the outlines, I like the blocky colors rather than smooth transitions, the more comic-booky look. (Plus that means a drawing like this can take 5 hours rather than 50... :P)
http://i.imgur.com/U0QAjpc.png
I added a few more touches after this on separate layers, the wind and the cold breath, as well as having the feet sink into the snow a bit. This is generally where the magic happens. This step is fun, easy and goes a long way to make the drawing look a whole lot better.
