If you want more power on your backhand, this video is going to explain a critical component to generating huge racket head speed which will translate to more power. When the "drop" goes into the "hit", you utilize gravity and momentum into your strokes which gives you easy power on your backhand groundstroke.
The timing, however, can be challenging. This video will walk you through the first 3 phases of the stroke: 1. The Preparation: During this phase, The racket tip is up, as you move your body into optimum hitting position, and are watching the tennis ball.
2. The backswing: Here your hands rise into the hit, and stretch backwards into the power position. 3. The forward swing: Here is where the drop happens. As you press forward off your back foot, your hips immediately begin to rotate into the court, and subsequently, your racket tip drops and goes right into the hit.
When you are practicing this sequence, initially you should think of each stroke in these 3 phases. And as you begin to master them, you can begin to think of them as one "organic" movement.