Firstly, getting the right direction to the smash. This comes down to court awareness and the position of your body and leading arm. Get any of these wrong and you won’t hit the part of the court you were aiming for.
Secondly to get more power, you need the strength and power in the muscles that contract in order to play the shot, so the shoulders and forearm muscles need to be worked. To help keep balance and direction strong core muscles are also vital for stability.
Thirdly you need to hit the shuttlecock at the right point. To do this you should always be behind the shuttle, so that you make contact with it directly in front of you, ideally hit at the highest point forwards of your racket shoulder.
Your wrist should be ‘cocked’ or bent backwards before the shot and then snapped forwards at the point of impact to hit the shuttle with maximum power. This should resemble a whipping action.
Finally in order to get in to the right position, you need the fitness and speed to be able to move in front of the shuttlecock to be able to hit it properly.
To do this you’ll also need to ensure that your feet are in a ‘front to back’ formation with your weight forwards so that the thrust can be made from the back leg which will propel you forwards as you hit and follow through with the smash.
One final tip that you can use for developing power in your smash is to try watching the racket actually hit the shuttlecock, this way you might be able to see where things are going wrong.
These are some useful tips for how to improve your smash in Badminton, but ideally you should work with a coach or invest in some training DVD’s to see exactly how to play the shot properly.