Sun is practically at home in the tenth house. Sun is considered a king among nine planets in vedic astrology. Tenth house deals with career and reputation. It also signifies father. In a favorable placement Sun could ensure that native becomes a great king, politician, top administrator, CEO, managing director, manager or one of the top level position in a given field. Sun is bright, charismatic, confident, industrious and cheerful. Tenth house is possibly the best place for it as long as Sun is strong. 

     Ofcourse like with all malefics Sun is "Sthana Shubham Karot, Drishti Hani Karot". In simple words it does good to the place where it is placed but bad to the house where it aspects. Sun from tenth house aspects the fourth house which deals with home, happiness, heart, mother, motherland, old age, land property and other important portfolios. And all these important portfolios of the fourth house suffer due to Sun's malefic aspect. If there are malefics associated, placed or aspecting the fourth house then the situation only gets worse. There is a good chance that old age could provide some troubles.

     According to B. V. Raman: "Native with Sun in the tenth house is successful in all that he undertakes. He/She is strong and happy and has sons, vehicle, fame, intelligence, money and power. They could be employed in government service". Sun in tenth house is also great for those who want a career in agriculture and farming especially for those who grow grains, pulses, flour, corn and vegetables. Sun's placement in tenth house may provide some frictions with dad especially if native is a male. 

     Generally speaking Sun in tenth house is a great placement for it. Just in case there are malefics in fourth house or associated with Sun in tenth house the native should pray to Lord Ram. Traits of Lord Ram like kindness, benevolent and obedient nature, empathy for subjects are the qualities that successful natives with Sun in tenth house need to cultivate. 

References:

Raman, Bangalore Venkata. How to Judge a Horoscope. Delhi: Motilal Banarsidass, 2014. Print.