Keep your elbows close to your torso at all times and maintain your body stationary.
Now, instead of curling the weight straight up, curl it back towards your body, keeping your elbows stationary and using your biceps to lift the weight.
Continue to lift the weight until your biceps are fully contracted and the bar is at shoulder level. Hold the contracted position for a brief moment as you squeeze your biceps.
Slowly begin to bring the bar back to starting position as your breathe in. Repeat for the recommended amount of repetitions.