"Other than standing around, what would the veterans teach the recruits to do better?"

In this type of warfare it seems to me standing around is a very big part of it. Not running away when a wall of bullets comes your way, step in line to take the place of a dead comrade... that sort of thing. Morale played a bit role, for certain. It always does, but here it might be the main diference (besides reloading speed perhaps) between two equally equiped and similarly trained units. Just my impression though.