Adjust the handles inwards then position the seat height so that the handles aligned with the lower chest. Then sit down and grip the handles ensuring that your for-arms are aligned with your wrists.
Start by pressing down until your arms are almost fully extended, then in a controlled manner bend the elbows back to just before the starting position to avoid clashing the weights. Tense your triceps throughout the movement and ensure that your elbows stay roughly in line with your hands. Repeat for the desired repetitions.
Avoid having your elbows flare out too wide when pressing.