how to deal with different people

  Recently I bought a book of Dale Carnegie-'how to win friends and influence people'& 'how to stop worrying and start living",the English version.Long time before I have read this book,I think it was during my college life but at that time I never thought too seriously about the relationship between different people.I took it for granted that people would treat the way how you treat them.But life is far different from that.Honestly often in my work and life have I felt confused and even desperated of the complicated human relationship.I'm not going to justify myself here that I have  done nothing wrong before,but there were moments that I was really unable to understand others.It seems there are people who never condemn themselves and every mistake is other people's faults.I myself is a very sensitive person,I can't allow myself to do anything that may bother others while I don't know how other people can have their concience feel quiet after they have done some harm to others.Such questions like this make me doubt my life pholosiphy--am I too naive or am I too immature? Or am I too serious that life is just a game, if you are too serious you'll just miss the funny part,the part people deceiving each other,taking advantage of others and sucking the superior while fooling the inferior? One word I heard in my work is "Da Tai Ji" which means people are good at shifting the responsibility to others and make themselves free from it.I always heard that it's a fine art to deal with different people successfully.When you have mastered this art you can manage everything smoothly.Then what's the essence of this art?
  Now I find it's really necessary for me to think over the principles that I need to follow to get along with people.So I turn to this book for help again and hope it can give me some suggestion.I'll appreciate everyone who can give me some invaluable advice.Hope we can discuss it here.