One way to get the players to get into a good body position and get used to making C's in the ice is to have them drop their stick and place their hands on the wall. In a good hockey position have them get used to making C's in the ice 1 skate at a time.
One of the biggest inefficiencies we see when players are learning to skate backwards is having two hands on the stick. Encourage players to release the bottom hand from the stick when skating backwards.
Another thing you will see quite often is players bending too much at the hips. This limits your mobility and vision of the ice in front of you. If you can get a player's eyes to look up then they will typically start to lift up their chest and head.
Another common flaw is players staying on their inside edges. The only time they should be on their inside edge is durig the push (carving the C). When they bring their skate back under their body they should be neutral (both edges).
Too much hip swiveling is another thing you will see a lot in young players. We want the hips to stay square and use the legs independently to push out in front and carve the C's.
Every once in a while you will catch a player with their weight too far towards their back. This puts too much weight on the heels and it is easy to lose balance. The weight should be on the balls of our feet.