If Mercury is located in first house of horoscope then you will be very clever. No one can cheat you easily. You can judge anybody. Your judgment generally does not go wrong. According to Lal Kitab this first house is owned by Mars and Sun. This way mercury will not give you good effect but it depends on the Zodiac in Ascendant.
Vedic / Indian Astrology says, Mercury and Jupiter becomes stronger in the first House of Horoscope. The position of both planets called as ‘Digbali’ in Indian Astrology. But my experience says if there is not Mercury’s bad Zodiac Position as Pisces, the Mercury would not make any bad effects to a person that much. Even in Aries and Scorpio, Mercury is not good but anyhow Mercury will give good results in satiety.
Mercury would be happy if there is Taurus, Gemini, Cancer, Leo, Virgo, Libra in Ascendant. Even in Sagittarius Mercury would be graceful for his / her partner. Because Mercury’s Own house is in the front. Mercury sees seventh house where Gemini is there. This way the person would have very good married life.
Jai Shree Ram !