Use both hands to grab the attacker by the shirt, at the center of the chest just below the collar or neckline.  The most effective way to headbutt someone is to draw them into a whiplash motion. In order to accomplish this, you need to push and pull the attacker away by the shirt. Avoid grabbing the attacker behind the neck. Natural instinct is to grab the attacker behind the neck and draw the head down for a headbutt, but the problem with this is that the neck and shoulder muscles naturally tense when grabbed behind the neck, making it much more difficult to pull the person forward. Use your full body weight to push forward into the attacker until their upper body leans back.  This movement causes the attacker to lose balance and causing their shoulders to disengage. Since this movement is also likely to be unexpected, you will also have the element of surprise on your side. As soon as the attacker's shoulders disengage, use your arms to pull the attacker back toward your head. With the shoulders disengaged in this manner, the attacker's arms will naturally swing open, preventing them from using the arms to block the headbutt. As you draw the attacker toward you, bring your head down so that the top of your head meets with the attacker's nose as their nose drops down.  Strike with the top of your head. Do not use your forehead. The nose is a sensitive pressure point, and striking it with enough force will allow you to knock the other person out.

How would you rephrase that briefly using Chinese?
抓住对方的衣领。 把他推开。 快速把他拉向你。 迅速的用头顶撞击他。