How to Build Social Capital and Community

I've talked about why we should do this, now we need to figure out how.
Need to recruit and grow network, but also maintain the bonds and sustain the community.
==Some speculation for now==
Mutual benefit.
Giving and receiving, generosity and gratitude, are supposed to help bond people.  Which makes sense, that's why people group together, it's mutually beneficial. So offering value is a good place to start. Especially in a social way, or in a context with social opportunity.
Interest, awareness, and trust are (I suspect) important key factors to gaining new members. See also: matching and alignment, and Who we can build social capital with.
One case is when people already have an interest that you can meet, and they simply need to become aware that your community exists.  In that case, once they are made aware it is very likely they will try to join unless they get turned off somehow.  Once they arrive, they will need an experience that suits their preference (I suspect niches/subgroups within a group will facilitate this best), so that they will want to stay.
Another case would be where people don't currently see your group as interesting to join.  Note that they may still see your group as an "ally", or potential ally, which can still be useful (for example, promoting/mentioning each other increases the chances of interested people becoming aware of your group). 
=== Just do what a community does? ===
I kind of think that building social capital and community mostly just involves doing what a community does. And it will grow and develop. 
== "Momentum" Strategy ==
For now, see this article.
==Possibly useful further reading etc.==
*Social Capital: Prospects for a New Concept (which is available free online)
*How to attract audiences: a radical rethink
==See also==
*36 Questions to Fall in Love
*Mutual benefit
*What a Community Should Do
*List of Social Divisions
*matching and alignment.