Shoulders and belly button should point directly down the fall line. If the shoulders are turned across the hill, especially in moguls or steep terrain, it is difficult to turn the skis back into the fall line. He was a pretty stiff fellow. Some hold onto a straight-up posture, some people get into a sort of squatting stance and never budge. Holding a stiff stance leads to sliding instead of carving turns.
Flexibility is key in skiing.
As the turn is initiated, the knees should flex forward strongly to put weight into the turn, setting the ski on edge. To move into the next turn, the weight must come off the skis. Humming your favorite song and turning to the beat is a good way to practice. You're flailing your poles. It's not uncommon to see skiers dragging their pole tips or waving the poles in the air as they turn.