In traditional astrology, the first house rules how others perceive you when they first meet you, your coping mechanisms to new situations, physical appearance, mannerisms, your outlook on life, will power, identity, and how you were received in early childhood.
Supplementing traditional astrology, the esoteric meaning of the first house is the aura (the feeling around the person), the emergence of the soul purpose, activities of the soul, remote possibilities of life, the struggle of the spiritual man/ woman to carry on, and spiritual goal.
In traditional astrology, the first house is the original placement of the sign Aries and planet Mars. In esoteric astrology, the first house is ruled by the sign Aries and planet Mercury. Another name for the first house is Ascendent (AC) or Rising, and opposite from this house is the 7th house or Descendent. The 7th house is known as the shadow house, the part of yourself that you don’t naturally identify with, therefore, project it onto your partners.
In addition to whatever your first house sign is, if there are any planets on the cusp of the first house they will greatly influence your personality. For example, if you have a rising in Leo and Mars on the cusp of the first house, you can be perceived as a person who is like royalty and likes to get things done with a bit of speed and or competitiveness.