#Avoidance is the Best Defense

Be aware of your surroundings. You're in a parking garage, fumbling with your keys, and you see someone running towards you, who appears less-than-wholesome? Run away! Someone pulls a knife on you? Run away! Do you have a choice between well lit, well traveled streets and dark, dangerous alleyways? Take the well lit, well traveled street. The best way to defend against a particular situation is to not get in it.

You can't hurt what isn't there.