I think that people I would call charming generally are people who just know how to make you feel important. They laugh at your jokes, make good replies and just treat you really well. They give you their full attention when you talk, like look at you and listen, not just look out of the window or stare at the floor. They think hard about their replies to text messages and always reply etc.
Bascially I think it's all about knowing how to get alone really well with people and make them feel special. It's not charming to lounge on your chair, with your hands in your jeans pocket and stare at the floor and grunt or nod your head in reply, it's the opposite.
Eh... know what I mean?