I've been doing a sketch a day; as a warm-up before I start my work. Getting into the habit of it was actually quite tough. I found myself noodling about too long, cutting into my actual work schedule. However after good dose self-discipline, they've help me so much. I get into the rhythm of things much quicker, not unlike physical warm-ups in sports.
Sometimes I finish a full piece in one sitting. Other times I work on a personal piece in multiple sittings. It's great fun and I'm glad I got into this habit.