Maybe this isn't my most valuable skill, but lately I've been much better at setting to a routine and sticking to it in the absence of external enforcement: "Do your readings for class over the weekend. Go into the lab to work on research several days per week. Go to the regular seminars. Keep up on RSS feeds and extra readings in the evenings." Naturally there are virtues to flexibility as well, but just floating through my day as an optimized routine and avoiding the problems associated with time-inconsistent preferences has really helped my productivity in the past few months.