Do you have hands? Excellent. That's a good start. Can you hold a pencil? Great. If you have a sketchbook, open it and start by making a line, a mark, wherever. Doodle.
Images from Hamonshu: A Japanese Book of Wave and Ripple Designs (1903) for Art Thursday. These seem like they could be good for doodling or zentangles (should I capitalize "zentangle"?).
A couple of posts that mention Zentangles (I'm capitalizing it this time, just in case).