First, reach up to the sky. Touch the clouds with your finger tips. After 10 seconds, lean to the right and hold. 10 seconds. Then to the left. Then bend one arm behing your head and hold your elbow. 10 seconds. Then the other. 10 seconds.
If you want, you can follow a short stretch/yoga video on youtube. Other stretch ideas: bend forward while sitting/standing, try splits and maybe a seal stretch where you lay down on your stomach and push off the ground backwards to stretch your back.