The trouble with milking cows, the pros say, is they don't stay milked. Same with small groups, they need constant attention. Like this: How to get people interested to join small groups? Ed Stetzer gives three tips, one of which is teach it biblically.
Prefer a podcast? 9Marks discusses such topics as Is there a biblical precedent for small groups? and Should small groups take the Lord’s Supper? (17:32)
Need resources? LifeWay has a plethora of studies for every type of small group. Check out Christianity Today's top ten small group Bible studies for 2018, including Life Lessons from Paul and Psalms: Managing Our Emotions. 12Stone has free resources for small groups, with more general church resources here. The church hosts the Maxwell Leadership Centre, if you appreciate John Maxwell (I do). And free brief videos about small group ministry, including meaningful prayer ideas for a small group (5:08) and asking follow-up questions (2:20) Oh, a parody from RightNowMedia, how to have an openly shallow small group.(2.19)
Great advice: making everything, including small groups, about life change, not attendance. (fr Dan Reiland's excellent 5 Ways to Help People See the Value in Attending your Church)