I have a 03 buick century what gear to use for normal driving?

I would like better gas mileage?I have a 03 buick century what gear to use for normal driving?It has an automatic transmision. Just put in (D) drive or the highest number on the gear shifter and make sure the overdrive is turned on. The transmission knows what to do.I have a 03 buick century what gear to use for normal driving?You want to use the "D" for drive, unless there is an overdrive option, which will give your vehicle the best MPG