Every day in August (save one) I've done a quick drawing in my sketchbook. I've limited myself to black ink, but occasionally I'll use white ink on black construction paper that I cut out and tape onto the next page. I usually do it very quickly before going to bed and this forces me to do something fast and just get something on the page.
It's become meditative. It's nothing fancy. It's mostly just lines -- particularly if it's late. But I'm addicted.