We know from the latest neuroscience research that our brains are programmed to "catch" the other person's delight and happiness whenever we see a genuine smile.  So…wait until you've been introduced, then as you shake your new acquaintance's hand and say her name, you smile broadly.  Body-language-savvy alpha leaders know this trick - it's as if you and your name brought a smile to their face.

- Janine Driver, You Say More Than You Think

Whether you're in customer service/sales or you are meeting people in a social situation, the friendliness you exhibit at the beginning of a conversation is always crucial.  Try the above tip during an initial greeting to set a better tone.  Smiling from ear to ear from before you meet someone until after they leave can feel very false and forced.  Instead, be more judicious with when you smile to make each smile mean more.