Sit down so your shoulders are aligned with the pivot points.
Gripping the handles, raise your elbows up to shoulder height.
Slowly lower to just before the starting position and repeat.
Using the wrists to lift the weights.
Using momentum on the way down.
Having shoulders too far above or below pivot points.
Adjust the seat height so that when you're seated with your chest against the padding, your shoulders are aligned with the rotation axis of the machine. Grip the handles evenly with your wrists aligned with the forearms.
Start by raising up from the elbows until they are aligned with your shoulders, then slowly lower back down to just before where the weights rest. Conduct the movement in a slow and controlled manner. Repeat for the desired repetitions then gently rest the weights down.
Avoid relying on your wrists to raise the weights or using excessive momentum.