There's a new way of doing CPR, which you can see and learn at: https://www.youtube.com/watch?v=E5huVSebZpM. The only thing i'd add is to make sure the heel of your lower hand is close enough to the chin to be on bone and not cartilage, because the cartilage can be broken off of the end of the bone. (Still, better a broken sternum than an untimely death.) Feel up and down the center of your own chest to familiarize yourself with the point at which the bone stops and the cartilage is attached.