Be both hedgehog and fox.
Know thousands of little details.
Know three big rules.

The book shows examples of small things city comforts that make urban life pleasant: places where people can meet, methods to tame cars and to make buildings good neighbors, art that infuses personality into locations and makes them into places. Many of these small details are so obvious as to be invisible. The book also discusses what the author calls the Three Rules of Urban Design. You can download a sample chapter at David's blog citycomforts.com