Tennis has become a power game. Because of this, many players are getting stuck back at the baseline or even behind the baseline.
It is extremely effective when opponents have assumed this more defensive position, to be able to hit balls low and up in front of them. The correct way to keep the ball low is to make contact early (out in front of your front foot) and keep the swing somewhat level with a shorter backswing and follow through. There should still be enough length of the swing to allow you to repeat the shot-it should not be short and quick.
My advice is to keep all of your focus on the point of contact and let the racquet follow the trajectory you are trying to get. The follow through should be slightly higher than the top of the net since your goal is to get the ball to cross the net two feet or so above the net. Keep in mind that the ball does not have to skim the top of the net to be effective.
This nice low, solid shot is extremely effective in doubles but is also a great shot to play once your deep, powerful shots have set the point up.