When I doodle, I try to keep the figures simple enough so I can focus on telling the story. But I agree they are very important part of a story.
How to draw a simple figure?
For those of you who'd like to be able to draw, but don't know where to start, a line figure (middle) is the easiest. As long as you can draw basic shapes like dots, lines, circles, squares, you'll nail this figure. All you need is a circle for the head, two dots for the eyes, a short line for the mouth, longer lines for the body, arms and legs, and shorter lines again for hands and feet.
Once you get comfortable with the line figure, you can move onto a more realistic figure, like the one on the left. You'll need a circle, dots, a line for the face. For the body, arms and legs, use modified & stretched rectangles. Try to make the hands and feet more realistic. Try different face angles by move the eyes and mouth around. There you go.
Once you get comfortable with that, you can practice your own figures, and gradually form your own style. On the right side, there's a little figure I usually use to represent myself. If you want to doodle a figure to represent someone, the first step is to think. Think what is it something that you remember from that person -- her/his face/body shapes, objects that s/he has, body languages s/he uses as well as the personality.
For example, I wear glasses and almost always have a pony tail, so that's what I always draw when I doodle my figure. I'm a fairly small size, so I'll draw it that way. Sometimes I like to be funny, so I don't mind drawing myself funny expressions or body languages.
If you are not sure, try to find characteristics from a photograph. Keep practicing, and I'm sure you'll be able to draw lovely figures :)
