Good manners reflect something from inside-an innate sense of consideration for others and respect for self.
Manners are like primary colors, there are certain rules and once you have these you merely mix, i.e., adapt, them to meet changing situations.
Custom is a mutable thing; yet we readily recognize the permanence of certain social values. Graciousness and courtesy are never old-fashioned.
Manners are made up of trivialities of deportment which can be easily learned if one does not happen to know them.