It is normal for cars to consume more fuel on initial startup on cold days.One thing to remember is that an engine always runs most efficiently when it is warmed to operating temperature. Now, there is not a lot of information in the question, but what I would do to achieve optimun gas mileage is insuure that the tires have the proper air pressure, a good tune-up including the air and fuel filters and have as less weight as possible. proper tire pressure alone will give you a noticeable difference in fuel economy.