Here is a recent commission I did! Included is a process shot to show how I managed to get it to what it is.
First I pose 3D models to help get a general feel for the where things are and how they should look. 
Second I rough over that and tweak things to fit the vibes for the piece.
Every step of the way is communicating with the commissioner as well so that they know the direction its going and to make sure that everything is a-okay.
After that its the usual for lining and rendering!
With the BG I tend to only paint the portions that you're going to see, so without the characters it looks a bit silly.... When everything is completely rendered, then I do several color layer modes and textures to adjust to satisfaction.