How to do properly classic rear delt fly?

1. Stand with your feet shoulder-width apart and hold a dumbbell in each hand.

2. Bend forward at the hips, keeping your back straight and core engaged.

3. Let your arms hang down towards the floor with your palms facing each other.

4. Slowly lift the dumbbells out to the sides, keeping your elbows slightly bent and your palms facing down.

5. As you lift the weights, focus on squeezing your shoulder blades together and exhaling.

6. Pause at the top of the movement and hold the contraction for a moment.

7. Slowly lower the dumbbells back to the starting position, inhaling as you do so.

8. Repeat for the desired number of reps.

It's important to keep your back straight and your core engaged throughout the movement to avoid injury. Also, make sure to choose a weight that challenges you but allows you to maintain proper form. Finally, remember to warm up before performing any weight-bearing exercise and stretch afterward to help prevent injury.