For instance, when you start a fire you start with your wood placed close together, concentrated in a stack or pyramid. This makes sure that the fuel is arranged neatly around the initial flame. You supply the first spark, often from a couple of different angles in case one or more goes out, and you use plenty of tinder, lighter fluid or other quick combustibles to make sure the fire takes hold.
Your content structure is your log pyramid. You keep it tight together, concentrating your activity where it can best take hold. Then you seed the site with initial content and known users to spark the discussion, often from a couple of different angles in case the some of them fizzle out. And finally, you pour on the gas through promotion to make sure there's enough activity to sustain the blaze until the larger conversation takes hold.
Of course, this is just a metaphor. Your community is made of people, not stacks of wood. But a successful community manager learns how to coax embers in the hearts of their members, nurturing the first wisps of smoke into a roaring blaze that spreads to others.
Is your community smoldering or sputtering? How are your fire-starting skills?