We've written before about the get more involved area and letting members apply their skills to the community (ABCD).
Kraut and Resnick suggest something even better. Create a list of things the community needs.
When members know what a community needs it offers them a chance to be influential within the community. It lets members feel important. It gives members a sense of ownership over the community. They are able to contribute their resources, skills, and experience in a meaningful way.
It's a very-simple way to motivate the community. Even better, you can actually get things your community needs. Perhaps you need a designer, some support at upcoming event, access to a ladder, or an expert on horticulture.
What if your community doesn't need anything? Then research what the community wants to do/achieve and what it needs to get there.