I believe awareness is the best method of self defense in "street" regards. Putting yourself in bad situations and thinking before you act are the best things to do. If you work late at night and park in an isolated area, walk do your vehicles in groups or have security escort you. Stay away from bad neighborhoods, especially after dark.
These are just a few things but I believe go along way in what self defense really is. Often if someone is getting robbed someone who is stupid and trying to play hero is going to get killed if the perp has a weapon, especially a gun. Some money or a few credit cards is not worth your life, give it to them than call the police. Instinct will generally let you know if they intend to harm you no matter what.
"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". -Cus D'Amato