As one of the 9 Traditional Feng Shui Cures, mirrors are considered the "Aspirin" of Feng Shui because they can cure so many problems in an environment. However, it is important to use them properly or you may end up receiving the exact opposite of what you wanted to achieve.
Feng Shui "Do's"
-Do use a "whole" mirror in which you can see yourself in one piece. This gives you a sense of confidence as you get one last look at yourself before you leave the house.
-Do hang mirrors to bring in the beauty of nature from outside. Nature has a way of lifting up your Chi energy.
-Do hang mirrors in a dark hallway as it will add light and movement to your space and bring the Chi energy down the hallway to help circulate it throughout your home.
-Do hang a mirror near your entryway to activate the water element.
-Do place a mirror against the wall that defines a missing gua from the Bagua. This will visually expand the space and symbolically fill in the missing gua.
Feng Shui "Don’ts"
-Don't hang mirrors that distort your image. Overtime this can make you feel less confident about yourself and it can give you a distorted view of yourself. If there are broken fragments of the mirror, these broken fragments in time can make you feel "Broke" (finances) or "Broken up" (emotionally). A whole mirror gives you a sense of confidence and completeness.
-Don't hang mirrors in the bedroom as they bounce the energy around the
space which will keep you up at night. (You can hang a mirror inside a closet door so it can be shut at night)
-Don't hang a mirror next to the bed or on the wall above the bed (LOL yes I had to put this here) because in Feng Shui it is said that if you can see your reflection in a mirror while lying down on the bed it will bring in a third person into your relationship. It also can startle you when you are waking up in the middle of the night which doesn't give you a good feeling.
-Don't hang mirrors to high or too low. It must be at a height where you can see your entire head and shoulders, and those of everyone else who lives in your home.