Run. Hide. Surrender. Fight. Die. Work in order from left to right, only going to the next step when it is obvious that the previous one won't work. Following these steps are a good way to defend your own life. If you have other goals in a violent encounter (such as defending your friends, or engaging in a predatory attack), this will not work so well.
Run. As Miyagi says, "Best defense, not be there." Rollerskates are the best defense against kung-fu. Proceed to the next step if you can't outrun your opponent (unless you can get to safety before they catch you). As a corollary, if you know where your opponent is going to be, stay alive by being somewhere else.
Hide. If you can't get away from your opponent, maybe you can keep him from noticing you. Put something opaque between the two of you. Maybe even put something opaque and solid between the two of you.
Surrender. As a Tae Quon Do class was practicing disarming assailants with pistols, a student asked the instructor what, personally, the instructor would do if somebody came up to him with a gun and asked for his money. The instructor immediately reached into his pocket and threw his wallet on the ground. Often, what your opponent wants isn't worth fighting over. Know yourself well enough to determine, at a moment's notice, what you are and are not willing to surrender.
Fight. Fight when you must, and only when you must. Even martial arts schools teach avoiding a fight. Avoid fighting at all costs, since there are no guarantees, no matter how good you are. A fourteen-year-old drug addict with a cheap .22 can kill a Navy SEAL with five years of training.
Die. Always an option, but almost always the last resort. Learning to better run, hide, surrender and fight will help keep you from resorting to this.