I don't ordinarily review two books at once, especially two by different authors, but these are both reference books in a sense, and both deal with the rules of etiquette in Australia.
In my opinion, given my own demographic, I found The Penguin Book Of Etiquette by Marion Von Adlerstein the superior book. It covers everything and is the more obvious successor to Emily Post for the Aussies. I've found this super helpful for those odd occasions when culture shock leaves me scratching my head.
Charm School: The Modern Girl's Complete Handbook Of Etiquette by Kathy Buchanan though, would be the better book for older teens, or those leaving home for the first time for university, first job, home, etc. This is the book for the twentysomethings and it's frank, honest, and slightly amusing in style; much chattier and looser than Von Adlerstein's voice. Note: This book is specifically aimed at women.