This stretch will strengthen your shoulders in the proper posture position.
To avoid injury, be able to perform these stretches with pain:
Intro. & Upper Body Stretches
And these strengthen exercises keeping your elbows below the shoulders:
Upper Back/Shoulder Exercises
The modified shoulder press will strengthen the shoulders and upper back muscles when you rotate your hands outward.
Here are the steps for the modified shoulder press:
Set your proper sitting posture.
Raise your weights parallel to your body.
Keep your elbows at 90 degrees, and below the shoulders.
Modification: Rotate your hands facing outward.
Raise your hands over your head, keeping your body still.
Lower your hands in the same manner slowly.
Repeat 4-5 times.