Street self defence isn't about flashy moves, roundhouse kicks and spectacular strikes! I've watched a few videos on You Tube where you see a guy in a street fight going into some crazy ninja stances. I wouldn't dream of doing anything like this and how ever highly trained you are this is asking for trouble.
The key basis of winning a street fight is to be in control of the situation. By 'win' I don't man we are out to walk away with the other guy on the floor. Winning may actually be simply walking away unharmed. I know that will shock some readers but that's the reality of real street situations.
Being in control means staying calm and talking. Keep your hands up in a guard position to prevent an aggressor coming into striking distance. Keep your voice pitch and tone in an assertive not aggressive range. Showing weakness to some people will give them an invitation to attack.
If you aren't able to calm the situation by talking there may come a time when a physical confrontation is the only option. If this is the case it may even be appropriate to strike first. Again I know this advice may surprise some people but if you are backed into a corner it really may be the best way out.
Traditional martial arts don't prepare us for real street fights. Most have their roots in ancient fighting systems when the world was a very different place. For example, aikido has its roots in the ways of the Samurai warriors of Japan. I have trained for many years in aikido and it's a beatiful, fluid martial art which after years of training can be deadly. That said I would not use aikido in a street fight other then perhaps the basic avoidance of a strike or perhaps a lock once I had taken control of the situation.
Street self defence is about using simple, direct techniques to shock and surprise an attacker. Some people may even call these dirty fighting moves. Of course you have to stay within the law in what ever way you deal with any attacker. It's down to you to assess the situation and use whatever force you feel is right and fair both for you and your aggressor. For example, if a harmless drunk is hassling you it would be unreasonable to use a dirty street fighting move to cause harm. However, if faced with a group of potential attackers, some possibly armed, I would say anything goes.