I have posted a PDF which explains The Three Rules of Urban Design. It's an extract from my book City Comforts.
Just click here to download it. (If the size of the file presents a problem for you, please email me and I will see what I can do.)
Practically and theoretically The Three Rules are the fundamental "pattern generator" for creating "city-ness." When it comes to figuring out how to make a walkable neighborhood or city, after The Three Rules everything else is epilogue.
UPDATE: And don't miss this animated GIF which illustrates the difference between "city" and "suburb." It's really quite amazing (and hard to believe until you start observing it for yourself) but the whole world of urbanism revolves around the location of the parking lot.