This exercise is very famous and really good for your triceps. You only need a dumbbell or resistance band.
Stand in a split-stance position holding a dumbbell with one hand. Contract your abdominal muscles and maintain it throughout the exercise. Your head and neck should be aligned with your spine.
Exhale and press the dumbbell overhead. Your elbow is pointing to the ceiling and it´s straight but not locked. Maintain your balance. So, don´t change the position of your head, torso, or feet.
Inhale as you bend your elbow in a slow and controlled way, lowering the dumbbell behind your head. Do not allow the upper arms to move. Continue to bend the elbows until your upper arms begin to move backward. Be careful with the back of your head.
Try to keep your upper arms perpendicular to the floor throughout the exercise and your elbows shoulder-width apart.