I'll tell you what doesn't work. Overbuilding the place. Staten Island is a tragic example of this. In Manhattan, it's like they're repaving the streets with park.
You need a certain amount of density. But the overriding purpose of the density is to be able to cram more stuff-you-want-to-do near your house.
Also, keep in mind that the "stuff" in stuff-you-want-to-do can be replaced with "people".
Yup. This has been borne out in studies of high-rise buildings as well - they just don't work to efficiently house large numbers of people, it ends up cheaper overall to put people in traditionally-sized houses.
You need a certain amount of density. But the overriding purpose of the density is to be able to cram more stuff-you-want-to-do near your house.
Also, keep in mind that the "stuff" in stuff-you-want-to-do can be replaced with "people".