A sustainable community would have all resources easily to the community; lots of alternative commuting options (bike, walk, public transportation), vegetation to keep the environment permeable and water sources clean, people willing to put in the time and effort to keep things working.
Many cities will need large amounts of restructuring to make this happen. If we renovate existing neighborhoods and build new neighborhoods to have more of these sustainable options, we need to start at the top with city planners to get the ball rolling.