This pose can be done at the end of any practice before finishing postures, as long as you’ve done enough backbends to warm up. To begin, lie flat on your back, bend your knees, and place your heels next to the outer edges of your buttocks. Bend your elbows, and with your hands in fists, place them alongside your head. The heels of your hands will touch the sides of your neck; point your elbows straight up toward the ceiling and allow them to gently reach toward each other. If this isn't accessible, you can set up the same way you would for Urdhva Dhanursana (Wheel Pose), placing your hands beside your ears and then coming up to your elbows to more readily enter the pose.
Take a deep inhale, and as you exhale, push through the legs to lift the sacrum off the floor about 4-6 inches. As you inhale, push through elbows and arms down to the floor alongside the head and clasp your hands together behind the head. If this isn't accessible, stay in Wheel Pose with the top of your head gently resting on the floor. Push through the elbows and draw the elbows isometrically towards each other and toward the sides of the head. This will engage the serratus anterior.
If you'd like to take the pose deeper, slowly begin to walk the legs out long, setting the toes on the floor and placing the inner edges of the feet together. Take 5-10 cycles of breath.
To get out of the pose: If your legs are straight, walk them back to the buttocks so the knees are bent. Lift the head first before lowering all the way down to the earth. Lower the spine slowly, releasing the sacrum last, on the exhalation. Straighten the legs out onto the mat in front of you, and come back to your breath.
See also 7 Mild Backbends That Feel Just as Amazing as Wheel Pose