Planets move in the sky in their orbits around the Sun. Since this path of their movement is elliptical (not circular), so their distance from the Sun/earth also varies. In this movement when these planets are closest to earth/Sun they seem to be the most illuminated. This position of the planet is called exalted. Same way when the planet is at the farthest position from earth it seems to be the least illuminated. This position is called debilitated. Planets are at their strongest and most favorable positions when placed in their exaltation signs while in debilitation they are at their weakest and least favorable situation. Exaltation and debilitation sign of any planet is always opposite of each other (180 degree apart) as given in following table.
Traditional astrologers teach it in very entertaining manner:

• When the king Sun arrives in the house of army commander Mars (1st sign) he gets the utmost respect (exalted) but if it arrives in the house of queen’s maid Venus (7th sign) it gets the bad name in society (debilitated).
• When queen Moon arrives in the house of queen’s maid Venus (2nd sign) it gets all the respect (exaltation) but same queen going in the house of army commander Mars (8th sign) it gets humiliated (debilitation).
• When Prince Mercury arrives in his own house (6th sign) it gets happy (exaltation) but child Mercury going in the house of teacher Jupiter (12th sign) feels sad (debilitation).
• When commander Mars arrives in the house of servant Saturn (10th sign) it gets all the respect (exaltation) but same Mars going in the house of queen Moon (4th sign) feels unwelcome (debilitation).
• When guru Jupiter arrives in the house of queen Moon (2nd sign) he receives warm welcome (exaltation) but same Jupiter going in the house of a servant (10th sign) it gets humiliated (debilitation).
• When female priest Venus arrives in the house of learned Jupiter (12th sign) it gets respect for its knowledge (exaltation) but in the house of prince of Mercury (6th sign) acts as a maid (debilitation).
• When servant Saturn arrives in the house of queen’s maid Venus (7nd sign) it gets all the fun (exaltation) but same Saturn going in the house of army commander Mars (1th sign) stands outside the gate (debilitation).
• When soldier Rahu arrives in the house of prince Mercury (3rd sign) it tells its stories (exaltation) but same Rahu going in the house of great Jupiter (9th sign) it gets humiliated (debilitation).
  

7 out of the 9 planets (excluding Rahu and Ketu) possess the lordship of 12 signs in Vedic astrology. As the tradition says (for explaining in a simple manner) the Sun and the Moon being the king and queen of the planetary kingdom were the rulers of all the signs but for sake of administration they gave the lordship of 10 signs to 5 other planets (excluding Rahu and Ketu). The Moon and the Sun (queen and king) kept 4th (cancer) and 5th (Leo) sign for themselves respectively. And then rest 10 signs were distributed to planets in the order of their visit to the King and queen. Out of love the Moon and the Sun gave 3rd (Gemini) and 6th (Virgo) signs to mercury (the prince) their son. The Moon gave the Venus (the female priest) 2nd (Taurus) sign and then the Sun gave 7th (Libra). Same way Mars gets 1st (Aries) sign from the Moon and 8th (Scorpio) from the Sun. Jupiter the minister and the high priest gets 12th (Pisces) from the Moon and 9th (Sagittarius) sign from the Sun. Saturn the servant gets the 11th (Aquarius) from the Moon and 10th sign (Capricorn) from the Sun. This way all the signs are distributed among the 7 real planets. Rahu & Ketu were rewarded by allowing them to usurp the rulership of the sign in which they are placed. Rahu and Ktu in any sign behave like the sign lord themselves.

Let’s understand the characteristics of these planets as they act according to their personalities. Once you understand them then you can easily understand how they give results in different houses. You can observe that the subject will have the most of the qualities of the planet that is ruling or sitting in the 1st house i.e. ascendant in his horoscope.
SunThe Sun has been conceptualized as king of the planets. This clearly means that the Sun should be understood to have the kingly ways. The Sun has dominance and ego of a king but the Sun is also protective of his people (friends and family members). Sun the king possesses leadership & desire to rule, management, an attractive personality, a royal nature, bravery, generosity, good intelligence, impressive authoritative voice, kindness of a father, heroism and fearlessness.  Physically the Sun is described with a square build, strong bones, curly hair, lovely appearance, medium stature, bilious nature, firm temperament. It is logical to say that the Sun in any house will give the results according to its own personality.
MoonThe Moon is described as the queen. So the Moon behaves like elderly women of high status. The Moon possesses the feminine qualities like vanity, kindness, affection, sensitivity, discriminating wisdom, restless nature, excessive sexual urge. But the Moon is not a young girl rather a wise elderly woman having the qualities of a mother so the Moon is also associated with motherly love. Moon is also associated with emotions, mind and mental peace. The Moon has a sweet and soft voice. Moon has a slim but roundish body, beautiful appearance, lovely eyes, sweet tongue, phlegm and wind in his composition, white complexion, short curly hair, amiable nature, Satwik inclination. Again it is logical to say that the Moon in any house will give the results according to its own personality.
MarsMars is the army commander so it possesses the characteristics of the same. Mars has the leadership with dominance, cruelty, a fierceness and aggression, desire to compete and win, possessive nature, manhood, sexual aggression, impatience and irritable nature. The voice of Mars is rude and full of audacity. Physiologically Mars is characterized by fierce eyes, short stature, athletic and youthful body, fickle disposition, curly hair, valorous nature, Tamasik inclination, readiness to hurt, irritability, bilious nature and fair complexion. Once again we understand that Mars in any house will give the results according to its own personality.
MercuryMercury the little prince is chatty with sweet voice and humor. Mercury the teenage prince has intelligence, logical & reasoning capacity, an inquisitive brain, jolly nature, naughty childish ways, instable but stubborn mind, desire of change & novelty and a capacity to play with words. Mercury has a slim and beautiful body, large eyes, beautiful young skin, medium height, Rajasik inclination, plenty of energy, bile, wind and phlegm in his composition. Once more Mercury in any house will give the results according to its own personality.
JupiterJupiter is described to have the personality of a minister or high priest with virtuous disposition. The high priest Jupiter is wise, knowledgeable, noble, distinctly intelligent, highly educated, rational and logical planet. Jupiter is also just, true, spiritual, calm and helpful being with keenness in religious practices and forgiving nature with a measured speech. Physiologically Jupiter is described to possess a big belly and a fat body, phlegmatic and calm temperament, Satwik inclination. Needless to say that Jupiter in any house will give the results according to its own personality.
VenusThe Venus is thought to possess the female characteristics. But unlike the Moon the Venus is the younger woman.  So it possesses also the characteristics like attraction for opposite sex, lust, sensuality, desires for beautiful things that attract, aesthetic sense and all sorts of material pleasures. The social status of Venus is the same as that of Jupiter but while Jupiter is responsible for external affairs of kingdom (life) the Venus entrusted with the duties of palace (home). Venus also is associated with high education, creativity, writing of poetry, a musical voice, wisdom and intelligence and religious things but unlike Jupiter Venus is not that much of noble character. Physiologically the Venus is very beautiful/handsome, of symmetrical limbs and dark curly hair, and has an amorous disposition. He has excessive seminal fluid, windy and phlegmatic temperament, Rajasik inclination, grace, vigor, and multi-colored robes. Venus in any house will give the results according to its own nature.
 SaturnSaturn has been conceptualized as the old servant (with only one leg) of the family. Thus Saturn is described with the qualities like responsibility, discipline but slow and fussy movements because of old age (lazy disposition), miser, cruelty, very thoughtful nature and detachment. The voice of Saturn is harsh. Saturn has a tall, lean and weak body, stiff hair and limbs, large teeth, windy temperament, Tamasik inclination. Once more Saturn in any house will give the results according to its own personality.
Rahu/KetuRahu (& Ketu) is the soldier (lowest and meanest) in planets’ family. So Rahu (& Ketu) has characteristics of aggression, anger, sudden disruption, mean behavior, intelligence, lust and all sorts of addictions. Rahu and Ketu are also described to be a shadow planet so Rahu/Ketu acts like the planet that is conjuct, aspecting with Rahu, or if nothing then Rahu (& Ketu) behaves as the shadow of its sign lord. Rahu gives the result of those planets but in an abrupt and extreme manner; that is the peculiarity of Rahu (& Ketu). Rahu (& Ketu) has an artificial behaviour in all respects including the voice yet it tries to imitate. Physical properties of Rahu/Ketu are the same that of the planet imitated by them. Rahu/Ketu in any house also give the results according to their own nature.