The most important thing, my father told me, which I have never forgotten, and which I have often put unto practice was: If you get into a quarrel with anybody, hit him first. "If you hit first, the battle is half-won," my father always said "Don't let him hit first. You hit him first."
"What's more," he never forgot to say, too "Usually one blow is all you need."
I found this to be true.