There is an ancient Chinese proverb which says,
A man without a smiling face must not open a shop.
There is another saying that ,
You are not completely dressed
Until and unless you wear a smile.
A sincere smile says : I like u,
You make me happy ;I am glad to see u.
Behind a grin one discovers a set of teeth,nothing else.
A sincere smile is infectious.
It lits the light of happiness around.
Keep always smiling ,it will solve ur problems.