One of my favorite self defense techniques is the headbutt. It's more devastating than strikes because the skull has more surface area and much stronger. It leads to instant knock out. Headbutts to the face can cut people's faces, break cheekbones, break teeth, break noses, etc. besides knocking out. Even if you don't knock out your attacker, the blood on his/her face will likely blind him/her. Headbutts are hard to see coming so they're hard to counter.