How to (re)build downtown?

Smart Growth America just released an interesting new guidebook, (Re)Building Downtown: A Guidebook for Revitalization, "a resource for local elected officials who want to re-invigorate and strengthen neighborhood centers of economy, culture, and history through a smart growth approach to development."

I have a long-standing interest in figuring out how to revitalize small, primarily neighborhood-serving commercial areas. As a general rule, retail development lags residential development - but why do some communities turn around their commercial districts faster than others? What, if anything, can local officials and community members do to help?