Align your heels at shoulder width apart, press your buttocks against the wall, and be sure your shoulder blades are touching the wall (this is more important than the tops of your shoulders touching the wall).  You may need to squeeze your shoulder blades together slightly to get them in a more natural position and align with the wall. This is sometimes called "opening your chest." As you get into position, pay attention to your head position. Notice whether or not the back of your head touches the wall. If it does not touch the wall, you have forward head posture, and it is likely that you suffer from weak neck muscles. Pretend that there is a string going from the base of your neck to the top of your head. Pull that string up from the top creating a longer neck. As the back of your neck gets longer, you chin should tuck in and down somewhat toward the back of your neck. This is correct neck and head posture. Make sure you are not simply moving your head backwards and increasing the curve of the neck. This is also improper posture. Focus on creating length in the back of the neck. This is your correct head posture, and you want your body to remember it. Return to this position frequently to review how your posture is changing.

How would you rephrase that briefly using Chinese?
背靠墙站立。 让后脑勺贴着墙壁，摆出正确的头部姿势。 保持这个站姿一分钟。