Last Shabbat we read Parasha Shoftim which contains many very important mitzvot. I attended the Shabbat morning service and was called up for the second Aliyah which, interestingly enough, concerns the Laws of Jewish kings.
http://www.chabad.org/parshah/torahreading.asp?AID=36236&p=2
Deuteronomy/Devarim 17
14. When you come to the land the Lord, your God, is giving you, and you possess it and live therein, and you say, "I will set a king over myself, like all the nations around me,"
15. you shall set a king over you, one whom the Lord, your God, chooses; from among your brothers, you shall set a king over yourself; you shall not appoint a foreigner over yourself, one who is not your brother.
16. Only, he may not acquire many horses for himself, so that he will not bring the people back to Egypt in order to acquire many horses, for the Lord said to you, "You shall not return that way any more."
17. And he shall not take many wives for himself, and his heart must not turn away, and he shall not acquire much silver and gold for himself.
18. And it will be, when he sits upon his royal throne, that he shall write for himself two copies of this Torah on a scroll from [that Torah which is] before the Levitic kohanim.
19. And it shall be with him, and he shall read it all the days of his life, so that he may learn to fear the Lord, his God, to keep all the words of this Torah and these statutes, to perform them,
20. so that his heart will not be haughty over his brothers, and so that he will not turn away from the commandment, either to the right or to the left, in order that he may prolong [his] days in his kingdom, he and his sons, among Israel.
It is clear that Hashem prefers that we do not need a human ruler but he allows us to appoint a man to rule the people and avoid anarchy. The king must not place himself above the people and must remain humble, restraining his desires for horses and women {physicality}. The king must be a good example for his people in order to effectively and fairly serve as their king.