Like Philli said, I think that humility is a big factor. If I could borrow a quote from Prince Caspian,
Quote:
"Welcome, Prince," said Aslan. "Do you feel yourself sufficient to take up the Kingship of Narnia?"
"I-I don't think I do, Sir," said Caspian. "I'm only a kid."
"Good," said Aslan. "If you had felt yourself sufficient, it would have been a proof that you were not."
Or if you, like me, prefer the movie quote, 
Quote:
Aslan: Rise, kings and queens of Narnia. All of you.
Prince Caspian: I do not think I am ready.
Aslan: It is for that very reason, that I know you are. 
I also think the the king needs to realize that the kingship and the power he holds isn't to benefit himself, but to work for the people. He needs to be willing to do what is best for them, even to the point of sacrificing his life, if the situation called for it.