The short answer: I don't
The longer answers: I start fires. Or I roll snowballs. Cluetrain was a fire. Still is. It took communication (not community) to start it. The four authors of that tome have only seen each other in the flesh, as a group, twice. If there's a cluetrain "community", I'm not sure what it is. A lot of friends and fellow-travelers, sure; but not "community". User-centric identity is a snowball. It's also a community, to the degree that it's organized, sort of.
Do check out Doc's thought-provoking posts on starting those fires, and rolling those snowballs. From the latter:
Tell ya what. I'm fifty-seven years old, and I've been pushing large rocks for short distances up a lot of hills, for a long time. Now, with blogging, I get to roll snowballs down hills. Some don't go very far. But some get pretty big once they start rolling.
See, each snowball grows as others link to the original idea, and add their own thoughts and ideas. By the time the snowball gets big enough to have some impact, it really isn't my idea any more.
Anyway, at this point in my life I'd rather roll snowballs than push rocks.
Update 12/03: Interesting follow-up post on using these metaphors, starting fires and rolling snowballs as starting points for community building.