1) Never ask a woman her age - especially if you have forgotten. Only ask when in dire legal doubt, and only when absolutely necessary.
2) Hold the door open for your party when entering an establishment. Also, hold the door open for any party that may be close behind yours, especially if they are of seniority.
3) Always remember to say “Have a nice/wonderful day/night” or at the least say “You, too” back when the clerk/cashier is done helping you/checking you out. Every little bit of cheer counts. Also, always say “thank you” when another person helps you, even if it is their job. There is hardly such a thing as “undeserved thanks”.