If a coach could fix one thing about a new player's game before anything else, it would be the grip. Not fitness, not footwork, not the swing. The grip, because everything else is built on it.
Hold it like a handshake, not like a hammer
The commonest fault is the frying-pan grip: palm flat behind the handle, racquet face permanently open. It feels secure and it makes a backhand physically impossible.
The correct forehand grip is a handshake. Hold the racquet by the throat with your left hand, turn it so the strings are perpendicular to the floor, and shake hands with the handle. Your thumb and index finger should form a V pointing down the top edge.
The backhand grip is a different grip
This is the part nobody tells beginners.
For a backhand you rotate the racquet slightly anticlockwise and place your thumb flat along the wide bevel of the handle. That thumb is what pushes the shuttle — the power in a backhand comes from the thumb straightening, not from the arm swinging.
Trying to play a backhand with a forehand grip is why beginners' backhands go three feet. The arm is doing all the work because the thumb is not in a position to do any.
You must be able to change between them mid-rally
Good players switch grip several times in a single rally, in the time it takes the shuttle to cross the net. It looks impossible and it is simply practice.
Start by doing it slowly, off court, while watching television. Forehand grip, backhand grip, back again. A hundred times. It becomes unconscious faster than you would think.
Hold it loosely
Squeeze the handle and your forearm tires within twenty minutes, your wrist cannot rotate, and you lose all the snap that makes badminton shots work.
The grip should be loose enough that somebody could almost pull the racquet out of your hand — and tighten only at the moment of contact. That tighten-at-impact is where a surprising amount of power comes from.
A grip that is too small forces you to squeeze. If your forearm aches after an hour, check the handle size before you blame your fitness.
The test
Stand still and play twenty gentle backhand pushes against a wall. If your thumb is not flat on the bevel, you will feel it — the shot has no push behind it.
Coaches at KGB will check your grip in the first ten minutes of a session. It is the least glamorous correction in the sport and the one that changes the most.