Stance

 Let's talk about proper stance's first.

In most cases you will be in a Neutral every day stance, you would look awfully strange walking around like your a boxer 24/7. Your neutral stance serves a purpose as well, simply put, your neutral stance makes you...well neutral. This is good because if there are any witness' to an attack, generally people can recognize who the attacker is simple by the body movements/postures.

The step up from the neutral stance is the High Guard stance. In this stance your body is turned at about 45 degree angle with your dominant side back, legs slightly bent and at shoulder width apart with your non-dominant foot in front. Have your hands up and out toward your opponent, (as if you just pushed them away) at around your eye level with a slight bend in the arms. You want your hands open and in front of you in order to deescalate the issue (you don't want to fight if there is no need). Believe it or not if you have a smooth tongue, you can literally talk them down out of their aggression or scare them straight depending on the situation, but let's assume that this is not the case. The open hands servers two purposes;
First - there is less of a threatening or aggravating appearance.
(Try standing in front of a mirror with your hands clenched, then opened and you will see what I am talking about)
Second - when your hands are open and in front of your body, it gives you a time advantage, because your hands are are up and ready to take action if needed.

Finally we have the Defensive stance, (*notice - that this is not called the "fighting stance" as many self defense courses and practitioners state. The rational is that, you don't ever want to "fight", you only want to control the situation). Terminology will save you from a possible criminal charge or a fine, that's right! in some cases YOU can be charged with assault. So make sure you pick your words carefully and keep your head straight, don't jump to conclusions.
*Consider this; a person confronts you yelling at the top of their lungs to give them the keys to your car, you "fight" him off and you give him a concussion, only to find out he was a mental patient from across the street, that suffers from chronic nightmares. There is a possibility that you can be charge with physical assaulting a mental patient. (yes, I want to scare you straight, because using violence almost always ends negatively, but obviously if you truly believe you life may be at risk then that is enough to move to the next section.)
The defensive stance holds close to the high guard stance, as you body is still angled at a 45 degree, with your dominant side back, non-dominant foot forward, knees slightly bent, and at shoulder width apart.
The difference in this stance is your arms, hands and head. You want to tuck your chin down and bring your arms up to "cage" your head (think of a boxing stance), this will cover the most important area's of the body or rather the more vulnerable. Here's an important difference for the boxing form your hands will need to be cupped NOT clenched. I know what your thinking...(well, why not clenched?) BECAUSE!...no, seriously, there are a few reasons why you don't want to clench your hands to make fists, but I will just mention the more important one's;
First - this is not boxing, your not trying to K.O. a person...remember control,
Second - with clenched fists it will be harder for you to change tactics if you need to, when you mind is set to punch it takes training to switch from striking to grappling,
Third - majority of people tend to tense up when your under stress from a violent encounter, so putting extra tension on your already clenched fists may lock your hands in this position.