This goes faster based on how much you've invested in sneak (more attacks will register as sneak attacks) and how strong your attacks are. You should notice Sneak start to level rapidly. When Hadvar/Ralof crouches down and hands you a bow sneak behind them and strike them continuously with your dagger.
Upon starting a new game follow Hadvar or Ralof through Helgen and grab the dagger on the table in the torture room.Also, if I've missed anything as far as power leveling tips be sure to let me know down below. Those looking to start new characters ought to find the information in here very valuable. I decided to post what I know about power leveling various skills to help you guys out.
