How do I stretch my mid-back?

A great way to stretch the mid-back is to perform the thoracic spine foam roll technique.  This technique helps to reduce the sensation of tightness in the muscles of the mid-back and improve the range of motion of the spine.  Here is how to do it:  lie face up on the floor with the foam roll underneath the mid/upper back. Next, place the hands behind the head and let the elbows fall out toward the floor while keeping the head relaxed but supported.  Last, raise the hips off the floor while slowly rolling back and forth and applying pressure on any tender spots for at least 30 seconds.

Squat with your feet as close together as possible, keeping your heels on the floor if you can; otherwise, support them on a folded mat.

Separate your thighs slightly wider than your torso. Exhaling, lean your torso forward and fit it snugly between your thighs.

Press your elbows against your inner knees, bringing your palms to together in Anjali Mudra-Salutation Seal: Press the hands firmly but evenly against each other. Make sure that one hand (usually your right hand if you are right-handed, your left if left-handed) doesn't dominate the other. If you find such imbalance, release the dominant hand slightly but don't increase the pressure of the non-dominant hand and resist the knees into the elbows. This will help lengthen your front torso.

To go further, press your inner thighs against the sides of your torso. Reach your arms forward, then swing them out to the sides and notch your shins into your armpits. Press your finger tips to the floor, or reach around the outside of your ankles and clasp your back heels.

Hold the position for 30 seconds to 1 minute, then inhale, straighten the knees, and stand.