What are the positive values and behavior from the character David from the book "I Am David" by Anne Holm?

As well as a great first name, David has a number of admirable qualities, which he displays at various points throughout the book. For one thing, he's incredibly brave. Escaping from a concentration camp and heading across Europe to find safety would be hard enough for an adult, let alone a twelve-year-old boy. But then David's no ordinary twelve-year-old. His terrible experiences of life in a concentration camp have made him mature beyond his years.
After the death of his friend and teacher Johannes, he completely cuts himself off from those around him, never permitting himself to develop any affection for another living soul. Now this may not seem a particularly admirable attitude to hold, but in the context of life in a concentration camp, it's crucial that David cultivates such a detached mindset. He knows that if he develops any kind of emotional attachment to anyone, then it can easily be broken as he and his fellow inmates are vulnerable to death at any moment.
So David figures that the best thing to do—indeed the only thing he can really do under the circumstances—is to concentrate purely on survival. Not only does this attitude help him endure the daily privations of the camp, it also gives him the requisite courage to embark upon his long, dangerous trek across the European continent.
As he proceeds on his journey, David continues to maintain his high moral standards, refusing for example to accept payment for a stranger for services rendered. The very fact that David has chosen to undertake this journey alone is a further indication of his strict value-system. He doesn't want to be responsible for getting anyone into trouble; this is his journey, and he will make it alone.
Despite the rigidity of his personal moral code, David shows that he has the capacity to change. And this is a further sign of positive behavior on his part. In due course he comes to realize that he can't do everything by himself; that he will need the assistance of others in achieving his goals. In doing so, he doesn't just learn to avoid death, but crucially to live life as well, to enjoy the simple things of life once more, such as good food and the joyous sound of laughter free from cruelty.