All of the above is correct, even the first half of Midchuck's.

As one who taught hand-to-hand combat in the Army, I'd also suggest:

1. Mental preparation. Realize that if you are attacked and fight back you WILL injure, and can even kill, your attacker. You can inflict anything from scratches to blindness to crippling to death, even if your intent is simply to get away. But if you are attacked, explode violently. This alone, as noted above, will cause many attackers to flee rather than get hurt. And scream "Fire!" while you're attacked -- it's more likely, especially in a city, to get help than simply yelling "Help!"

2. Work against the weak spots. For example, if you are being choked from the front with both hands, bring your hands (clasped togther) up between the bad guy's arms and explode them outwards. This will rip his hands from your throat by "working against the thumbs" -- the weakest part of the grip. If you're choked by an arm from behind, turn your head so that it lies parallel to the baddy's arm -- this will prevent him from pressing on you windpipe and cutting off your air.

3. You needn't be a Black Belt or Master. Learn a half-dozen USEFUL things and learn them so that they are second nature to you. It's all very well to be able to deliver a round-house kick but it's of no use at all if you're grabbed from the rear! So forget the movies and TV and go for the useful instead of the showy.

4. Don't go where you might be attacked, run if you can, fight if you absolutely must, and if you fight, fight to win by hurting, crippling or even killing.

5. Put not your faith in gadgets, from guns to pepper spray. Put your faith in yourself and your own abilities.