I think that this phrase " Try to make at least 4 people smile each day" is something that would mean for you to be nice to people and respact them , that way they will be pleased with your stay and like you. Of course , the first person you should put a smile on is , well, yourself. By being happy , positive and supportive you will send this good vibe and happy emotional state to everyone.
So , in conclusion, This phrase means for you to be nice to people and be nice to yourself.
