If you smile to most people, they will be inclined to smile back. If you can attact lot of people in your life, then you can easily find out who can become good friends (like common interests, etc) and who can't. Of course, some people of the opposite sex may find your smile like a way of flirting. So, early in the friendship, you need to decide, whether a possible romance with a certain person is what you want from him/her. I believe that slowly you will be able to attract the people who make the types of friends you like to have.