There are many opinions on this subject and of course they are all different. True aggression is actually not that common in dogs. If given the choice in most situations a dog will try to escape when they are faced with a situation they perceive as a threat. The aggressive behavior happens when they feel trapped and have no way to escape. In most cases if you give your dog an escape any aggressive behavior will end pretty quickly. The key is catching the warning signals they put off before it is too late and they have already begun trying to protect themselves.
It is extremely difficult to reach a dog and accomplish any change in behavior once they have gone into survival or protection mode. So as soon as you see them start to tense up, move forward in the direction of the threat or any other cue immediately change direction with them and walk away from the threat. If you do this your dog will begin to be comfortable and will not behave aggressively any longer.