Penalty killing situation:
The most efficient way to play this situation is by using a triangular formation (the circled players shown in the figure), where two penalty killers play low to cover the deep attackers and the remaining penalty killer plays high to cover the opponents point men.
If the puck is moved behind the net (see figure), do not go behind the net because the majority of time you will lose that battle to the opponents out front!

When the puck is moved behind the net, play the percentages and force the puck carrier to make the first move. Generally in this situation, one of the attacking defensemen will move in toward the slot for a shot. (RW) should constantly read the positioning of the attacking point men as well as the puck carrier behind the net. He should move to the slot along with either defenseman and communicate with his team mates along the way.
When you gain control of the puck, freeze it, skate with it, or shoot it down the playing surface. Either way, you knock precious time off the clock.