When I don't want to think too hard about what I'm making (i.e. doodling), I find myself drawing in circles. Their fluidity is satisfying, and I've trained my brain/hand to move cyclically without too much effort. I've been thinking about habits a bit lately while reading The Sweet Spot (highly recommend!). Habits are fabulous, but in certain realms, I need to keep it fresh -- especially creatively -- and stepping outside of the usual keeps my brain agile, flexible, alert.
This one's called Sphere of the Unknown.