What are examples of principled behavior that the book teaches the reader?

I think that most of the moral lessons are ones that come
through Bruno.  For example, when Bruno listens to Maria's story and recognizes her as
more than a mere maid or servant, the lesson here is that the more we recognize other
people in their own predicament, the greater the chance our humanity is enhanced.  A
similar moment happens when Bruno recognizes that Pavel, the man who tends to him after
he falls off the tire swing, is a doctor.  The idea that individuals are complex,
possessing narratives that might lie past our own identities, is something that Bruno
again teaches us.  The most intense example of principled behavior and moral conduct
probably emerges through his friendship with Shmuel.  Bruno is able to understand that
there is more that makes human beings the same than that which divides or separates us. 
When he crosses the fence into the side in which Shmuel lives, he looks no different
than his friend.  When Bruno is scared of life in Auschwitz, but valiantly continues the
search for Shmuel's father, it is a moment whereby we see the importance of standing up
for that which is right and honorable.  It is here where I think that the most intense
example of ethical conduct is relevant.  Bruno stands up for his friend, at ultimate
cost to himself.  In this, one realizes the transcendental power of friendship and care
for another and how important it so not take the form of the world around an individual
when it fails to uphold transcendent notions of the good.