Don't try to be the expert on everything. Allow the Holy Spirit to speak through others as well as yourself. Let the questions do the work. If possible, when someone says something, say what they said back to them in a different way, and ask if you understood correctly.
Learn to be comfortable with silence. They are thinking, not sleeping. (Hopefully) Let others answer first.
Don't try to do too much at once. It is better to have a lot of short sessions than a few long ones. It gives the Holy Spirit time to work on people's hearts and minds between meetings.
Allow members to choose their own seats. This small but important detail ensures members will feel comfortable in the group.
Establish the Bible as your authority. You are only the facilitator of a group, the Bible is the group's authority and the Holy Spirit is the Teacher.
Establish and clarify expectations. Members have certain expectations for one another and for the facilitator as they journey together. Discuss the following possible issues during your first group session: Privacy, start and stop times, attendance, talking on point, interrupting, voluntary participation in discussions, hand raising, etc.
Be a good example. Be positive and encouraging when people contribute something. Don't let anyone feel stupid. Don't be surprised when they don't know something. They are there to learn.
Questions to ask to keep the discussion going:
Can anyone add to that?
Can anyone give me an example of that?
Can you be more specific?
What do the rest of you think about that?
That's really interesting, I'm not sure I've heard that before. Does anyone else have a different way of looking at that?
Always remember to start and end with prayer.
If the size of your group gets so large you are running out of time for everyone to talk, consider making it two groups.
Plan from the beginning to work yourself out of your role as facilitator by training up the next group leader as you go.
Don't let the same one or two folks monopolize the sharing time each week. If you see this start to happen, before the next class ask their assistance before the group time to get others involved. Say something like, can you help me bring out more of the quiet people? Giving people time to write down their answer to the "Think & Pray" questions before starting the discussion should help keep dominant talkers from becoming too much of a problem.
Trust the Holy Spirit and remember it is His class