My dad would be very proud of the tip for today. In fact, I think most dads would. This is one of those tips that your father always told you to do, but, to be honest, you never figured out the reason for until you were older.
Change the Oil. In fact, this tip really includes all general maintenance (air filters, tire rotations, etc.). Time and again it has been shown that, when a car is properly maintained in a general way, that car gets better gas mileage.
If someone changes your oil for you, it is worth the couple of extra dollars for a "full service" visit. They will check all the things that need checking to insure good mileage. If you change your own oil, don't forget to check the other things as well.