Learn from other hosts by lurking or participating on other lists. As I said above - some books, some practical experience, plus a reading of some theories of community. I also draw on my own imagination and ideas to think of new ways to handle problems and stimulate interaction. I see it as part of my managerial role with trAce. I also get personal enjoyment from reading and participating.
Online communities are just such a natural environment for people to gather around.
I'm not sure how many years I can sustain logging on several times a day as i do now, but expect to continue to be a regular user.