I think the two main points would be already mentioned regular "what are you playing" posts and just writing yourelf whenever you have a chance. I think that livier communities encourage engagement while "dead" ones make people less willing to participate as that means they'll more likely to become the center of attention and not everyone is comfortable with that.

Personally, I've been meaning to write some posts about the stuff I played recently but just didn't have time to do so. Maybe this week...