I don’t think there is a best way. I think there are tools for engaging people and in different circumstances different tools work better than others. I agree that the focus should be positive that is why I think it is important to talk to the person and find the ways in which they do already care about the environment. Environment is a broad term that includes people, places, plants, minerals and various forms of media. When you define the environment more broadly it is easier to find the shared values and identify the way those values are enacted in the person’s day-to-day life. This creates the ground for engaging the person so as to water the wholesome qualities of sustainability in whatever form they happen to arise.