Whether I am working with animals or with people I like to get to know them, personally. That includes imaginary characters as well as those in real life.
However, with the imaginary ones it is hard to 'see' them unless I create lots of preliminary sketches on paper and in the computer. And here I can see the subtle differences that must not occur in the final sketches or paintings. Consistency is the keyword.
Once I have a good idea of who is who, I will print out a collection like this one and go back to the drawing board with pencil or pen and continue the process until I really know who these people are. They will become my friends, and I often find that they are in part based on people I have known. In this case I was well acquainted with all three of the real people that eventually made their way into this imaginary world.
I am sure that often happens to other illustrators. Does it happen to you? How do you arrive at the final destination for your characters? If you have time, post your thoughts here *:)