One of the best exercises I’ve come across for loosening up and brainstorming for drawings I learned at school in Seattle: the China Wall exercise. Ideally, you shut yourself in a room with only a stack of 100 sheets of newsprint, ink, a stick or brush (or your face, or toes; whatever…), and a pot of coffee (or drug of choice), and not leave the room until there is something on every single one of those pieces of paper.
Your drawings can be representational, they can take two seconds to make, you can spend an hour on one if you like; the point is to basically puke your brains out onto the paper and free up all of the things that stop us from the pleasure of just drawing. Shunryu Suzuki says something very profound on this release and non-attachment in his book, Not Always So: Practicing the True Spirit of Zen:
“Each one of us knows how to go to the rest room without attaching to something we have in our bodies. When we realize that we already have everything, we will not be attached to anything. Actually, we have everything. Even without going to the moon, we have it. When we try to go to the moon, it means that we think the moon is not ours.” (44)
So, basically, this is your brain taking a crap. Something which I personally know I need to work on a great deal.
See some of my work fueled by these exercises here: stasiab.etsy.com