When I get home from work, I set a timer and draw for fifteen minutes. I usually pick a photograph, or a cartoon, from the internet. The resulting drawings aren't anything but exercises in the study of observation and proportion, but those are important things to study. When I get out of the habit of doing them every day, I find it really difficult to warm up when I'm drawing something else. But when the opposite is true, and I actually draw daily, I'm often amazed how easy lines and forms and new ideas spring out. If you're new to drawing, and even somewhat serious about it, people are going to tell you to draw every day. Listen to them, especially if you're feeling discouraged about drawing. The benefit I got from just two or three years of daily drawing is amazing, and personally very satisfying.