In a fight it's best to hit your opponent hard once, where it incapacitates them and then to beat the soft parts of their body, where it hurts them for weeks, so they never want to fight or mess with you again. If you don't punish them some and just quickly incapacitate them, they almost always want to fight again. Hitting someone in the face, more than necessary, can easily get you in legal trouble, both with the authorities and lawyers. Hitting the gut or the back below the shoulder blades, off center of the spine, inflicts long lasting pain, with minimal signs of damage and doesn't usually damage your hands. The inside of the thighs is a good place to hit people too.
Whoever seriously hurts the other person first, almost always wins a fight and will always win the fight, if they press their advantage.
I've had the best luck knocking people out by hitting them where the neck and head come together. Sternum punches are good too because they drop and badly scare the person you hit, because they can't breathe.
The first guy i ever took out with a sternum punch was a 6' 3", 265 pound drug dealer, who was on our wrestling team, who also sold butterfly, knives, throwing stars and porno magazines on the buses. He was trying to make a Baptist girl perform oral sex on him on the bus and was being very foul to her. She was crying. I intervened and punched him once in the sternum, when he shoved some paper down my shirt. He fell to the floor and layed there gasping for a couple of minutes. I made him apologize to her and promise to leave her alone, while I stood on him.
A few days later he hired an Australian guy to fight me. I hit that Aussie once in the left side of his neck and then beat him worse then I've ever beaten anyone else in my life. He could not walk fully upright for weeks and missed over a week of highschool. I got in absolutely no trouble over it, because the bus driver heard him accept the money.
Keith