Rough animation must be drawn with easy and quickly, with minimal amount of lines but with as much information as possible. Drawing can have only a couple of lines or seem dirty, but you don't have to make it clean just yet. Only after you've found all the keys, you can re-draw those frames with more details and clarity.
Here are some rough keys examples:
On the first animation stage you need to remember about liveliness of your drawing, about gesture, condition and expression. After you've thought through your animation you can do clean-up. First comes the animation, the form - only second.