Here's a quick warm-up I did one day before starting inking. I often like to do these since they help my drawing chops. They also help loosen the forearm muscles as well as get blood flowing into your hands. I've found that my inking is greatly improved when I do a warm-up.
This is from a reference photo I took of a great friend of mine and a beautiful woman named Laura Siruchek. I had the picture up on the screen and I started with a colored pencil and watercolor paper. I think it took me around 30-45 minutes to do. As you can see, the point is to do a loose interpretation of the reference and catch the likeness but not make are refined, tight drawing.
