Mercury in astrology is some what like water as whatever color you adds in water, water becomes of that color. In the same way, when Mercury is associated with benefic planets, its tends to act as benefic planet and when it is associated with malefic planets, it tends to behave as Malefic planet.
Mercury signifies sisters, mental intellect, analytical and logical abilities, Telecommunication, communication, education, humor, lawyer, Publishing and printing, Content writing, Business, stock market, liver, hair and skin allergies, nervous disorders.
For Aries, Mercury in 1st house will make one witty, humorous, intelligent, knowledgeable as well as communicative but at the same time can give health problems to the native as Mercury is 6th house lord.
For Taurus, Mercury in 1st house will be good for progeny, family life, financial life, education as well as native will be of good character, provided, Venus is stronger as well.
For Gemini, Mercury in 1st house will be good for domestic happiness, gains from im-movable assets as well as for good Marital life
For Cancer, Mercury in 1st house will be bad for health related matters. One might had to travel at distant places for his/her profession and might have some issues with brothers or sisters.
For Leo, Mercury in 1st house will be good for financial gains and family life too. One will get respect in society and will get helps from friends circle too.
For Virgo, Mercury in 1st house will be good for professional as well as for marital life. One will get respect in society as well as name and fame too.
For Libra, Mercury in 1st house might takes native to foreign journeys and one might work abroad to earn his/her bread and butter. Further, one luck prospects will also be quite better and one might be charitable too.
For Scorpio, Mercury in 1st house will be bad for financial gains and one might had to face obstructions in his/her professional and personal life. One might had to avoid all kind of work, that can give disgrace and dejections. One might had to take proper care of valuables at home too.
For Sagittarius, Mercury in 1st house will be good for marital as well as for professional life. One will get name, fame and respect in society too.
For Capricorn, Mercury in 1st house will be good for getting success in competitions, spirituality, family travels, getting respect in society as well as for luck prospects too.
For Aquarius, Mercury in 1st house will be good for progeny, education matters, love life as well as for inheritance gains too but at times, native might had to face obstructions too.
For Pisces, Mercury in 1st house will be bad for domestic happiness, marital life, education matters as well as for marital life.