1. Sit in chair with out armrests is best
2. Raise arm over head
3. Lean in the direction opposite to the arm that is raised
4. Go as far as you can comfortably.
5. Hold the stretch and breath
6. Breath 3 times and feel your side from your shoulder to your hip open up
7. Come gently back up right and lower your arm
8. Repeat the stretch for the other side and repeat this side and the other side again.
Why I think of this as a forgotten stretch is from the patients I see every day.
When I massage the back and notice the tension of the Erector Spinae Group of muscles next to the spine and move onto the areas following the line of the ribs, Quadratus Lumborum (the lower back), Obliques (abdominal waist muscles) - The muscle tension tells me and the discussion tells me that the stretch that would help has been forgotten or maybe never learned.
Most of our stretch education is usually from way back when- maybe high school, maybe from videos with some terrible examples being way back in the 80's when the bouncing stretch was popular but a bounce is not a stretch at all. A move that is done repeatedly with action and force is an exercise to build a muscle, not a stretch to assist the muscle to lengthen back out releasing the fluids and tension that is holding and shortening the muscle.
After doing the side bending stretchs move into the stretch for the lower back, mid-back/rhomboids and hip.