Do a very basic breathing exercise (there's one on the forum somewhere) and settle yourself as though preparing for a meditation.
Stand a couple of feet away from the mirror so that you can see your head and shoulders clearly.
Gaze softly into your eyes for as long as is comfortable.
When you have finished do something such as making a cup of tea or washing your hands to ground you.
You may experience a number of things when doing this such as:
Darkening of the face
Face blurring or appearing to alter slightly.
Eyes appearing to change colour or shape.
Shadows or mists appearing around you.
Seeing colours around you.
Seeing small lights or orbs.