Here's a little shoulder routine I did Monday last for someone with shoulder issues and to help with posture correction. It's great for strength with mobility as it covers a variety of movements.
It might be a little hard if you spend long periods sat at a desk or hunch a little.
You can always have you back against the wall every now, this will serve as a marker to see how far the arms are from the wall.
Use light weights or everyday objects, the other day we used a bottle of olive oil with a bottle of water :)
Have a great day, great Christmas and all the best for the New Year..
Keep well, stay active
Francis