90% of the outcome in a street fight depends on what you do before it starts. Actually, most of them are ego-based, and can be resolved by verbal and non-verbal de-escalation (calm talk and non-threatening body language).
If the situation spins out of control and you can’t help fighting your opponent, set up your first strike carefully. Keep the attacker busy talking, thinking, processing what you’re telling him. Use this time to determine where and how to strike. Land a hit while he’s still talking, and make it count!
The same psychological technique can be useful when the opponent holds a gun to your head or a knife to your throat. By talking to him you will distract him, get his train of thought away from cutting you or shooting you in the head. Once the distraction has worked, make your move!