Pushing with your dominant shoulder will give your stroke added pop and penetration.
 
PROBLEM 
Your forehand lacks depth and power. A possible reason for this is that in an effort to increase racquet-head speed you prematurely whip open your front shoulder. This pulls your racquet toward the center of the court and away from the point of contact, compromising the power and control of the swing. Your shot can deteriorate further when you’re in a pressure situation.

SOLUTION 
Instead of looking for more pace by swinging harder, focus on pushing your dominant shoulder toward the incoming ball. This action helps you lean your body into the shot while helping you retain stable posture throughout the stroke. Now the momentum of your swing is going in the direction of the target rather than off to the side. This gives your forehand added pace and penetration, two elements that will increase your chances of hitting an effective shot and taking control of the point.

Article by By Juan Nuñez, Photo by Manuela Davies/Double Exposure – Tennis.com