Begin with your palms firmly pressed on a bench and your feet placed on another bench or something of similar height.
Keeping your back close to the bench to reduce stress on the shoulders, lower your body by allowing the elbow to bend.
Drop until your upper arm is parallel to the floor and your arm forms a 90 degree angle. Press through your palms and squeeze your triceps to go back up and complete the motion.
To make it easier keep your feet on the floor instead of another bench. Start with your legs straight out. Creep your feet in closer to your body to make it even easier.
To make it more difficult have a partner gently load weighted plates on to your lap. The motion remains the same.