I think one of the challenging parts for people in lag putting is that they are still focused on the hole and making the putt. One drill that I use and find very effective is to lag putt to the fringe. By taking the hole out of the practice session it truly allows the player to focus on distance control. The drill is to try and get as close to the fringe as possible from anywhere on the green. It is also effective because it doesn’t interrupt with other players on the green, you can pick the shot as it’s not determined by where the cup is and there are unlimited angles and distances you can choose from.