6. Destroy the attacker.

Keeping an iron grip on the attacker's arm, you must immediately destroy him with vicious strikes. Head butt him in the face, knee him in the groin or side of the leg, bite him in the jugular if you must.

Remember, he is trying to kill you. You are therefore legally and morally justified to use lethal force. Once you have weakened him with strikes, attack his windpipe by crushing or striking it. You are not finished until he is down on the ground and not moving.

Nick Drossos shows many good videos on YouTube addressing this situation. (His language is pretty vulgar at times. If that bothers you, just use the mute button. But what he is teaching is right on.) Watch how he deals with a knife attack. Notice how he uses parries and simple strikes to counterattack:

7. What about a "static" knife attack? A static attack is when the attacker holds the knife directly on you (like at your throat). A "ballistic" attack is when the attacker is slashing or thrusting at you. Here Nick shows his defense against a knife being held at his throat:

Notice in every situation the defender redirects the weapon, controls the hand or arm (not touching the knife, but keeping it as far away as possible), and then works on disarming the attacker.

Two more videos from Nick Drossos deal more with defenses against static knife attacks and someone concealing a knife:

And finally:

If you successfully defend yourself (that means you live and the attacker has left or is on the ground), immediately call for the police and seek medical attention. You may be severely wounded and not even feel it.

If you are serious about defending yourself, you must train. Get a training partner, get some training knives (NOT "real", obviously!), some eye protection, and probably a helmet and protection for your throat and start practicing. You will fight like you train!