While you are in a ready position, you must take some small steps. If the shuttle is being hit is high, you must make more little steps towards the shuttle.
If the shuttle goes flat you do less steps but your racket must follow the shuttle. Normally you will do 2 small steps.
The final step before hitting the backhand clear, you will need to take a bigger step and then bang!
In short, small steps, small steps, look, look and bang! Just like a combination while playing Street Fighter. Enjoy the video and learn it!