If you spend long hours sitting, hunched over your computer or phone, your shoulders have likely adapted by rounding forward, it also does wonders for your posture. 

Such as this, Inverted Pushup. How to: Start in an upside-down “V” position with feet flat (narrow stances as necessary), hands pressed into the floor, and hips in the air. Bend elbows out wide to the sides bringing head to touch the floor. Press through hands to return to start. That’s one rep. Complete 10 reps. Repeat twice more for a total of three sets, resting only as needed. From there, continue on to your next move. (You're doing 10 total.)

You can also try other methods, or you can use this product to help yourself. It is a speed running training shoulder harness. If you are interested in it, you can try.