I mostly doodle when I'm in class and it's a lecture day. Believe it or not, doodling really helps me concentrate and I don't get bored. :) However, these doodles were not done during a lecture. There was more of a point to them. Plus, I don't have any of the doodles I did during lectures in digital form.
Other similar exercises involved never taking your pencil off the piece of paper, looking at an object for only a brief moment and then drawing it without looking at it again, or trying to draw something blindly without looking at your paper.
These two girls are from a phase I went through where I wanted to be a fashion designer. So, I was looking at fashion designer sketches and they all looked so effortless and beautiful. I wanted to be able to draw like that as well. Suffice to say, although I feel that these girls turned out pretty, they don't look effortless, or loose, but I have never been loose with my drawing. I like control. That's probably why I draw mostly with pencil and not oil paints. These girls were doodled with crayon. :)