Marking the ball with a line allows you to aim the putter face correctly to the target
Controling your ball from the rough so that you can actually hit the green requires a steeper swing, gripping down slightly and a tighter grip so that you can keep the clubface square and a minimum of grass between the clubface and the ball
Start with a neutral grip making sure that your left hand is not turned over or under the shaft, this will prevent you from manipulation the clubface at the top of the backswing