Against the assault of laughter nothing can stand.
-- MARK TWAIN
There's no question that smiling and laughing are clear indicators of how much you are enjoying being with someone. When the occasion and the subject allow it, always be quick to smile and laugh. A genuine smile involves the muscles that surround your mouth and your eyes. When you smile, make sure you get all of your face to smile. Let it go right up to your eyes. Now I don't mean grinning like the Cheshire Cat at everything that's being said, or laughing at every mediocre quip or joke. Overdoing it could raise suspicions that you're being phony or too openly trying to curry favor.
Remember also that smiles that appear genuine don't "switch off" abruptly. Real smiles seem to linger for a moment or two. A smile that doesn't linger really isn't a smile. There are very good psychological reasons to allow yourself to smile and laugh easily and naturally. Here is an illustration.
In my earliest days as a theater director, the very first comedy I directed was one by Neil Simon. It was a Broadway hit loaded with funny lines and a delightfully entertaining cast of characters in amusing situations.
When the cast and I got together to read through the play for the first time, we all slapped our thighs, held our ribs, cackled, howled, and generally reveled over Neil Simon's wizardry. During rehearsals and as the days went by, we all laughed less and less.
A few days before opening night we completed a run-through of the performance. It went smoothly and was word perfect, but it was flat. Nobody in the cast, including me, chuckled, tittered, or even cracked a smile. It was like we were doing Ibsen rather than Simon. I sat there wondering what had been so funny in the first place.
Opening night there was a full house of dignitaries, critics, and well-turned-out theatergoers. I sat in my usual place in the back row on the aisle (so I could leave in a hurry if the audience turned ugly -- just kidding) and have never been so anxious. The lights dimmed, the curtain went up, and the play began. Within minutes, the audience began to laugh and laugh and laugh, and what was most interesting -- I was laughing, too! How come? It was the same stuff that I'd heard during three weeks of rehearsal and that I'd quit finding funny, and yet here I was laughing again -- why?
The answer was infection. Smiling and laughing is very infectious. I laughed because they laughed, which refreshed my memory of what I had found so funny before.
I went many times to see that production, my first successful attempt at directing comedy, and I laughed almost as much at every performance I saw.
There's a lesson here for everyone. When you charm, you are being the audience for other people and the infection rule is just as true. When you smile and laugh, others will be inclined to smile and laugh right back at you.
A caveat: Watch out for people who smile with only one side of their mouth turned up. One should be cautious about lopsided smiles -- they could be half-hearted or less than honest.
The next time you are in a conversation, wait for the right time to show a smile as the conversation dictates. If the conversation and speaker are serious, you look serious. If the talk is about light, amusing things, encourage yourself to smile.
You don't necessarily have to agree with what is being said; you simply have to match the other person's mood. If she is being enthusiastic and you want to charm, allow yourself to smile with her enthusiasm.