Ascendant Sign in a horoscope is most important...

True personality and nature of an individual can be known from the ascendant sign in the first house of the birth chart, If its Aries (no.1) the person is physically active, if not generally active but surely as and when physical action is required such a person would be right there performing his task, normally good in sports On the negative side can be of angry nature. If the ascendent sign is Taurus (no.2), the person is of generally middle height but with large sign bone structure and somewhat stubborn also and of generally angry nature, also practical, intelligent, also can be dominating nature. If the ascendent sign is Gemini (no.3), such an individual is mentally active, also seems to have good talking power, possibly knows various languages, intelligent, likes to socialize, on negative side may not faithful. If ascendant sign is Cancer (no.4), person is definitely emotional, prefers to stay more
indoors than outdoors, normally has few friends, is close to his/her mother, also can be studious, likes reading, on negative side can be too emotional and sensitive, can have tendency to slip into depressed mind frame. If ascendant sign is Leo (no.5) such an individual has a big heart, takes interest in variety of things, has a good group of friends, likes to socialize, on negative side can burst into anger, egoistic, dominating. If the ascendant sign is Virgo (no.6), such an individual normally is always concerned about future, is also mentally active, intelligent, practical but is also pessimistic to some extent, also such an individual has quarreling nature. If the ascendant is Libra (no.7), the individual likes to socialize, likes shopping, likes to party, but is also capable to strike a balance between being practical and a party animal. Has good judging power. On negative side may not be able to keep hold on his checks and balances. If the ascendant is Scorpio (no.8), such an individual is a deep thinker, very passionate, inclined towards spirituality, philosophy, psychic things. But is also a hard worker and again to an extent of angry nature. If the ascendant sign is Sagittarius (no.9), such an individual loves to socialize, normally has many friends, is also inclined towards spirituality, religious practices, loves freedom, on negative side can be egoistic. If the ascendant sign is Capricorn (no.10), such an individual is very much practical, clever, down to earth, first comes duty and then everything else, on the negative side can at times become stubborn and look at the negative side of life. Fault finding can be in his nature. If the ascendant is aquarius (no.11), the person likes to socialize, normally optimistic, inclined towards spirituality and psychic things,loves to talk, prefers to go with the flow, but also takes interest in variety of things particularly music and art, on the negative side is not so practical and may end up trusting wrong people. If the ascendant sign is Pisces (no.12), such a person is generally optimistic, likes to meet everyone with a positive attitude, is also emotional, romantic, can be found to mentally very active, on the negative side has tendancy to slip into depressed frame of mind. 

But again to mention that placement of different planets in the horoscope also influences the nature of person but majorly the ascendent sign describes how the person is in eyes of others. And the placement of moon describes the mental state, the qualities will be again same as mentioned above as per the zodiac sign but the mental side will be more known to the person himself and less to the outside world, but the ascendant sign can clearly show to the rest of the world how the person is.

Now further, there are certain planets which are exalted in some signs and debilitated in some, Sun is exalted in aries and debilitated in libra, moon is exalted in taurus and debilitated in scorpio, mars is exalted in capricorn and debilitated in cancer, mercury is exalted in virgo and debilitated in pisces, Jupiter is exalted in cancer and debilitated in capricorn, venus is exalted in pisces and debilitated in virgo, saturn is exalted in libra and debilitated in aries. This also shows to an extent that If ascendant is aries (no.1), sun if not in libra and placed anywhere else will generally give only good result to such an individual, If ascendant is taurus and moon if not placed in scorpio and placed anywhere else will give only good results, if ascendant is capricorn and if mars is not placed in cancer it will generally overall give only good results, if ascendant is virgo and if mercury is not placed in pisces and placed anywhere else will give only good results overall, if ascendant is cancer and if jupiter is not placed in capricorn and placed anywhere else will give only good results, if ascendant is pisces and if venus is not placed in virgo but anywhere else will generally give good results overall.