My personal favorite pass-time and form of image-making has, and always will be, my sketchbooks. I carry at least one sketchbook on my person at nearly all times and have done so since about sophomore year of high school.
The first sketchbook I ever fully filled (and didn't loose or abandon) happened that same year. I told myself that if I wanted to be a working artist, I had to make art. And I had to learn to practice... a lot.