How ambitious should a Christian be? According to Luke 16:13 (ESV):


  No servant can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and money.


It seems to me that God gave us the desire to pursue certain things for a reason to begin with, so being successful and enjoying your career isn't necessarily a sin in and of itself. Is this the correct attitude?

How can a Christian keep God in the center of his or her life and properly enjoy worldly ambitions (such as a successful career)? Is there anything wrong with being focused on your career?
It's important to maintain an eternal perspective.  Enjoy your career, sure, but keep in mind that your career is over once you're dead, but eternity lasts forever.  As long as you keep your priorities straight and you're willing to give up your career if God's plan calls for you to do something different, you'll probably be all right.

Remember to keep Luke 18: 29-30 in mind:


  29 And he said unto them, Verily I say unto you, There is no man that
  hath left house, or parents, or brethren, or wife, or children, for
  the kingdom of God's sake,
  
  30 Who shall not receive manifold more in this present time, and in
  the world to come life everlasting.