I agree with Sento.
When you throw a straight punch, you've gotta think of your fist as the rock and your shoulders as a catapult. When a catapult fires, the rock never moves first - the whole fucking contraption does, and the rock is the last thing to be flung into the air. Same shit when you're punching - the feet turn, then the hips, then the shoulder, and finally the fist.
Same think with a hook, except it's more a mace instead of a catapult ... the killing end always moves last, and you whip it with the rest of your body.
It takes a long time to master, but when you do, you get some serious killing power - especially at close range.