Steven said it all, but let put a few more words with that
http://www.youtube.com/watch?v=YnFh_N5zATo&feature=fvw
Relaxation, form and timing are the most important things for power. Look at Silva’s last fight. For training in addition to punching, Olympic lifting could not hurt nor could general conditioning. For Olympic lifting and boxing you need a real coach, the most important thing past oneself. Good Luck