There are heaps of theories on this question - man and woman have pondered this for centuries and this is the reason many people turn to faith - to give guidelines for living ethically. The buzz at the moment if for something called "the secret" or the law of attraction. This law states that whatever you focus on you will attract eg if you keep saying "I'm fat", the universe hears the word fat and makes sure you get more of it. If you focus on being poor you will get more poverty. If you want to be rich and successful then you need to focus on this. 

• Always wear a nice set of clean undies. That is in case I get hit by a bus carted off to hospital and they strip me off in order to operate.  
•  Law is life itself and not the rules of its conduct. Evil is a transgression of law, not a violation of the rules of conduct pertaining to life, which is the law. Falsehood is not a matter of narration technique but something premeditated as a perversion of truth.   
• As far as you can, keep your eyes focused in the right direction; it is inevitable there will be dark moments to blur your vision.   
• Be objective as you look at life; never be pessimistic, for each day will present a new opportunity for you to attack the problems that defeated you yesterday.   
• Try to discover as much about yourself as you possibly can.  
•  Never take yourself for granted; many persons have lost battles because they did not discover the tools within themselves to dig to victory.   
• Be patient with yourself in the midst of your mistakes, for even the greatest minds of yesterday have been known to err.   
• Never be afraid to travel roads that are not familiar to you; many accomplishments have come as a direct result stumbling.  
•  And for those of you that may wish that none of the bad moments of your life had happened, always remember that so do all that live to see such times pass through their life....but that is not for us to decide.  
• All that you have to decide is what to do with the time that is given to you.