What does Rivka teach the newcomers to the camp and why was the information important?

In The Devil's Arithmetic, a young Jewish girl named Hannah is temporarily transported back in time to the Holocaust so that she will understand the suffering that her older relatives went through. She takes on the role of a girl named Chaya, who turns out to be the girl who saved the life of Hannah's aunt Eva.
When Hannah and her relatives are taken to a Nazi concentration camp, she meets a girl her age named Rivka, who has already been in the camp for a year and has lost most of her family. Rivka is a very resourceful girl, and when Hannah and others first come to the camp, she teaches them:
Not to lose their food bowls, because they won't be given replacements
That they can hide safely in the midden, where garbage is put
To stay away from the door of the ovens 
To pay attention to the numbers on others' arms 
Not to talk while working 
To organize things (meaning to steal food, clothes, etc. to help other prisoners) 
To do nothing that will make them stand out, because being noticed, especially by Commandant Breuer, will get them chosen for execution.
Sticking to these rules has helped Rivka survive, and she knows it will help her friends survive as well.