1- Sit upright on a flat bench (or you can stand up straight, with feet shoulder-width apart), holding weight plate above your head.
2- Left the weight up, till arms are straight and elbows close to head, this is your starting position.
3- Now lower the weight plate behind head as far down as possible while keeping elbows and upper arms in position.
4- Raise the weight plat up again to the starting position, and Repeat.
Tips and advises:
1- Keep the elbows together, don't allow them to flare out.
2- Try not to swing your body forward while performing the exercise.
1- Dumbbell One-Arm Triceps Extension