Tyrion was the first, I think. The main thing I’ve learned is to not draw using symbols: for example, I tried to use lines to render hair on Tyrion and Gandalf (that’s supposed to be him, yes).
Instead, try to reproduce regions of light and shadow, and proportions, faithfully.
You should be able to view them in “original” resolution by clicking on them. I think Cersei and Father of the Year turned out the most interesting.