There are those of us who simply cannot keep the pen separated from the paper, even when we have little time to create a masterpiece. The English language has coined a term for this. We call it doodling.
Even in an art form that is defined by quick and hurried sketches, some people (myself unfortunately not included) can create beautiful and unique artwork, simply by touching a pen to paper and watching what happens. I have chosen a few of my favorite doodling styles to list here.
While working with lined paper may not be preferable, some find a way to work around it, and even incorporate it into the doodle, such as these two pieces.
Another recently popular form of doodling is Zentangles. These are made by dividing a ground into blocks (or other shapes), then filling each section in with a different repeating pattern. They can be done in black & white of color, and each one ends up looking unique.
thelonelymaiden.deviantart.com
Another common doodle includes a word or phrase, usually relevant to the design in some way. Bonus points if you can make it into a shape, like this very interesting elephant.
sound of the river 