The hook is another power punch. Like the cross, it uses a lot of pivoting to generate power. You’ll see the hook thrown many different ways, sometimes with a horizontal fist, vertical fist, wide, short, to the body, and so on. Proper execution of the hook starts at the feet. Pivot the ball of your lead foot (as if you were putting out a cigarette), your knee, hip, shoulder and arm at the same time. In other words, they turn into the punch at the same time.
Your punching arm should be held at a 90 degree angle, that is, your forearm should be at a 90 degree angle from your bicep. Your punching arm should be parallel to the ground. And your fist should be held vertical. Remember to keep your rear hand on your face for protection.
To throw the hook with a horizontal fist, perform the technique above but put a corkscrew motion into the punch. If you are unsure what the corkscrew motion is, refer to The Jab. When throwing a hook to your opponent’s body, be sure to bend your knees slightly. Take a half-step in the direction of the hook, as if you were slipping a cross to the outside. Do not lean forward at the waist! If you do, you will expose yourself and make it difficult for yourself to retreat if your opponent tries to counter.
Here’s another view on the basics of the hook.