What can go wrong with arabesque? I see back legs unstretched and turned in, with little attempt to turn out from the hip. As a child I was always told that the arabesque must be the longest line you can make from the tip of the middle finger of the hand extended in front to the big toe of the raised leg. The middle finger should be in line with the middle of the forehead.
Another golden rule I was taught is that in an arabesque the shoulder of the front arm is never lower than that of the side arm. Think of second arabesque—how often do you see the waist collapse and the front shoulder drop? The side arm should be extended to the side and slightly behind the shoulder line. Often, in order to get the shoulders square, students lock the arm in the shoulder joint instead of extending it freely from the joint.