My system of getting books returned on time is that I am always reserving books. I usually go to the library once every week or so, and the library I go to has three week checkouts. So, when I go I pile up all of the books I checked out last time and turn them in when I'm picking up my reserved books. Otherwise I'd put it off until they were late. BUt I'm always eager to see the books they reserved for me, so I move on it faster than I would otherwise.