First House or Lagna House in Vedic Astrology shows One's generalize nature,a worldly view towards you,how world , in better way Society will look towards You . It shows one's personality and prominent characteristics of an individual can be predicted by analising first house in your JanmaKundali or BirthChart.
It also indicates physical body,mentality on superficial level (not subtle mentality/mind), one's liking /disliking,passion towards a particular subject. It is also  indicates ones carrier / business as First house is Seventh from Seventh House(indicator of Business ,dealings,partnerships etc) and is 10 th from 4 th House
 which indicates Ones mind, inclination towards particular profession.
Lord of the first house is called Lagnesh.
Planets in first , its degrees and degrees of first house also the rashi (zodic) and influence of other planets in birth chart on first house along with their aspects , together sums up Ones First House.
First house also indiacates head,wife /partners of your partners in partnership(opponents, business),brothers of Your friend,death of your enemy,long distant journeys of your son ,courage etc
A strong first house will give native name,fame, money ,sound health if it is not under malefic influence.
by malefic influence , I mean if there is one or more malefic planets placed in first house or If lord of first house is under influence of malefic planets like saturn ,rahu ,ketu, sun  and mars.