How we change what others think, feel, believe and do
Ask them about themselves
Ask them something about themselves.
If you do not know their name, then start there.
Compliment them about their appearance. Ask them where the got that nice suit, watch, hat or whatever.
Comment on their cheery condition, ask them why they are looking a bit down. Say they look distracted and ask why.
Ask if they have family, the names of their children, how old they are, how they are doing in school and so on.
Ask about their occupation, their careers and plans for the future.
Ask about hobbies, interests and what they do with their spare time.
Pay attention when they give you an answer. Show interest not only in the answer but them as a person as well, possibly evoking a betrayal response.
And when they tell you something, show interest in it. Follow up with more questions.
You look thoughtful. What's up?
What are you going to do this weekend?
That's a lovely jumper, where did you get it?
The most interesting person in the world is me. I can talk about myself all day long if somebody asks me the right questions and seems to be really interested in what I have to say.
Note that the level of intimacy in the questions depends on the level of relationship. Be careful also with sensitive subjects. If you sense that they are uncomfortable with what you have asked, apologize as necessary and change the subject.
If you ask questions but do not follow up, then then they may conclude that you are not really listening and are false in your apparent interest.