Your erector spinae muscles, or your extensor muscles, help extend and rotate your back. So the best way to stretch them is to curl your body forward and do rotational movements.
The first stretch is the cat/camel stretch. Get on all fours in a quadruped position. Arch your back upwards while you are tucking in your chin. You can hold the stretch for 30 seconds and do three, or you can hold them for 3 seconds and do ten of them. Make sure you are tucking in your chin to get the best stretch.
The next stretch is a double knee to chest on your back. Lie down and bring both knees up to your chest by grabbing either around your knees if you don’t have any knee issues, or underneath if you do have some knee issues. Then tuck in your chin and hold the stretch for 30 seconds, three times. Some people like to rock in this position to get an extra stretch.
Finally, sit on the ground with your feet straight out in front of you. Take the leg of the side you want to stretch, and cross it over the other leg. Then twist your body toward that side, and place your opposite elbow on the outside of that knee for the stretch. You can push on your elbow to get a better stretch. Hold this for 30 seconds and do it three times.
