Three major precepts:
Livable, predictable, legible, and open urbanism is good for everyone in it. It helps people contribute to urban life.
Cities are alive
A city is a living thing, not just in the poetic sense, but also in the literal sense of having a metabolism. Cities create themselves.
Just as all living things do, it needs rules well-crafted to keeping it alive.
If we are guided by principles, then we have chance at better outcomes than if we don't. I subscribe to the Charter of the New Urbanism, among other sets of principles.