Upper Back Doorway Stretch
Stand facing the doorway with your feet pointing towards the side of the doorway you will use for the stretch. Then grab the doorway (or other similar height object) a little below shoulder level with the hand closest to the doorway.
For example, if you want to stretch the right side of your upper back, face the doorway and point your feet towards the left side of the doorway and grab the doorway with your right hand. The goal is to stretch the back of your shoulder and upper back, by pulling/rotating your body away from the doorway.
This can be tricky at first, but a key is to hold on hard enough so that you don’t let go, but then relax the rest of your arm as much as possible, so you don’t fight the stretch. The other key is to maintain good upright posture throughout the stretch. Rounding your back decreases the effectiveness and/or makes the stretch move to a different part of your back
If you don’t feel much of a stretch, you can change your foot position to give you better leverage to pull against the doorway. Additionally, you can use your other hand to push against the doorway to increase the intensity of the pull.