Select a suitable weight dumbbell and sit in a preacher bench. The bench should be adjusted to a height that comfortably supports your upper arms and elbows without you needing to arch your back. At this height, your mid-lower chest will touch the back of the preacher bench.
Your feet should be planted firmly and your core is tight. Your lifting arm is outstretched on the pad taking the weight of the dumbbell in a palms up grip. Your non-lifting arm is either on your thigh or on the bench, helping to support your balance. This is the starting position.
Commence the movement by curling the dumbbell up from the elbow joint and squeezing your biceps. The elbow should remain fixed on the bench pad while you exhale through the movement. Do not lift the elbow or use momentum to throw the dumbbell up.
When your biceps are at maximum contraction and the dumbbell approach your shoulder, squeeze for a second and then reverse the movement by extending the arm to the starting position, inhaling as you do.