My town government agreed a few years ago to adopt the sustainablect.org framework, which has a bunch of green/sustainable elements I am really excited about.

Once the town agrees in principle to a framework, you can advocate for policies based on that framework, and mobilize people who are particularly interested in one issue (say, composting!) or another (sidewalk networks! green energy!)

The trick, I think, is to find a framework the town government is willing to support (in principle) with specific changes. The fact that there's a certification program to go along with the framework that has prestige is really helpful. But really, the core of it all is to find a bunch of folks in your community that want to push things forward towards a goal with a shared vision. Which means that ultimately community organizing is what makes it possible, in my experience.