Centre Street Church is the largest in Canada. CSC generously uploaded their small group training manual online, 96 pages of gold, including the "four spaces" explanation -- insightful.
A Kansas church did the same; their training manual is here, 40 pages. It lists icebreakers, games and great study resources at the end.
The book Eight Habits of Effective Small Group Leaders features these: Dream, Pray, Invite, Contact, Prepare, Mentor, Plan, Commit. They're worth walking through with group leaders. A pastor developed Q&A lessons for each habit. I'm using his material at ROOTS and recommend it.