I picked a lot from these material, but let me just share few:
Firstly, A community manager is not or shouldn't act like a customer care agent. If you answer every single question instantly, people become lazy and expect you to do all the talking.
Secondly, Sometimes, you need to just SHUT UP and wait. When you stay quiet, it forces other members in the group to start talking and helping each other out and this goes a long way in the status of the community from my experience in other communities.
Lastly, Don't answer everything. Only jump in if there is a big problem, a bad rumor, or if the group is brand new and needs a push. Otherwise, LET THEM TALK