A winged scapula is usually as a result of weakened shoulder blade stabilisers, especially the Serratus Anterior. The serratus anterior is also known as the punching muscle.
To target the Serratus Anterior directly, scapula protraction exercises work best along with serratus press exercises. Any movement which protracts the shoulder forwards at the end range of movement will target the serratus anterior. Punching a punch bag will also work this muscle.
Start with the end of the band in one hand at shoulder height, elbow bend. Push the hand forwards, straightening the elbow as you go, in a punching motion. Ensure you push through the entire shoulder, trying to reach as far forwards as possible. Slowly return the hand to the starting position under complete control.
Start in a lying position as shown, with a medicine ball in both hands, elbows straight. Keep the elbows straight throughout the exercise. Push the ball up, using only the shoulder girdle to move it. Lower the shoulders back down and repeat.