It helps to use both feet . Again, this sounds simple enough but you would be surprised. Beginners often lean way over to the right or left putting all of their weight on one foot while the other one skips tenuously off of the ground as the skier accelerates down the hill and eventually blows up in a cloud of snow and ski gear. Expert skiers often appear to have their boots glued together which inevitably causes some combination tail waging and arm flailing. The basic idea here is that a skiers center of gravity should always fall halfway between their feet for greatest balance, just like when you are standing still.
Skiing IS movement over terrain change so the glue-footed skier is usually out balance.
Just knowing that skies should be kept about shoulder width apart helps many skiers. The shuffling of feet exercises above are also extremely effective at targeting this aspect of skiing. L ook where you are going. When you walk you look where you are going, not where you are or where you have been. The same thing applies to skiing.