Have you read “How to influence people and make friends”?? There is a chapter on smile and Do you know how essential and important is your smile? You can do miracles by the way you smile. Suppose an acquaintance of yours entered the room with all dull face and worried and another person entered with a smile. Whom would you remember and would like to talk again among person stated above? Obviously the person who entered the room with smile. You can smile and make lots of friends and can crack the deal with your potential clients. When you make the other person feel important then there are chances that he or she would agree to your terms and conditions.Dale carnigie's book suggest us to smile no matter what but that ardent philosophy was limited to 20 th century and now this is 21st century and by merely smiling won't give you what you want because cynical people think that when you smile then there must be some personal interest  behind that and they will not pay you attention.When you smile all day then that smile is common for all and people will take it for granted and so if you think that by fake smiling you will get money from their bank account then you are wrong. Then what will do? Here i know i have confused you whether you should smile or not. There is no doubt in it that you have to smile but how to smile and when to smile that will play the crucial part whether you will engrossed your target or not. You should not start smiling as soon as you meet new person, first you have to scan that person and know his personality then smile and here i am talking about wave of smile that will touch your eye to eye and then that person will feel special that you are really Intrested  in meeting him or her. all i mean to say is you should never give a quick smile that won't give the best impression. First you know about other and then give smile. You have to do all this in delay of a second. 

Your smile also gives signal to your brain that you are happy at the moment and you can fool your brain to release happy hormone. 

I wish you all a life full of smile. bye.