When practicing, you should stretch and lie flat (preferably in the gym, there are instruments similar to narrow benches). When using dumbbells as birds, try to press your open arms down so that your chest muscles can fully stretch your shoulders.

In short, we should pay attention to the flexibility of ligaments when practicing muscles, that is, stretching. As for relaxation, I think it's very good to gently jump to shake the muscles and then pat them with your hands.