What points of chess etiquette does Waverly learn from Lau Po in "Rules of the Game"?

Waverly learns not to be vain or childish when playing chess. 

Waverly first plays chess after her family gets a used set for Christmas.  It is missing pieces, and her mother wants them to throw it out at first because someone else didn’t want it.  Her brothers are interested though, and Waverly turns out to be quite the chess player.  Her mother decides to let her pursue the game, telling her to make sure...

Waverly learns not to be vain or childish when playing chess. 

Waverly first plays chess after her family gets a used set for Christmas.  It is missing pieces, and her mother wants them to throw it out at first because someone else didn’t want it.  Her brothers are interested though, and Waverly turns out to be quite the chess player.  Her mother decides to let her pursue the game, telling her to make sure to learn the American rules so that no one can take advantage of her. 

Waverly sees a group of men playing chess in the park and wants to join.  When Waverly first approaches Lau Po about playing chess, he teases her by saying he hasn’t played with dolls in a long time.  He lets her play though, and he teaches her the finer points of the game. 

From Lau Po, Waverly learns all kinds of chess tricks and their names. She loses a lot of Life Savers, but she also gets better and better at the game.  In addition to fine-tuning her understanding of the rules and learning gambits, Waverly learns the "finer points" of chess etiquette. 

Keep captured men in neat rows, as well-tended prisoners. Never announce "Check" with vanity, lest someone with an unseen sword slit your throat. Never hurl pieces into the sandbox after you have lost a game, because then you must find them again, by yourself, after apologizing to all around you. 

Waverly says that by the end of the summer she has learned all she can for Lau Po. He was a good teacher, but she was also a good student.  He learned that she was more than a doll, and she learned that you get a little bit better with each opponent and each game.  A good chess player is able to incorporate failure and learn from it.  Waverly does that.