Be very comfortable with yourself and who you are. Guys like it when you be yourself. Make conversation with them, as if they were any other friend. Ask them about themselves, and laugh at their jokes/attempts at humor. It's very flirty and it makes them feel good about themselves. Really, though, you shouldn't be trying to impress the guy, the guy should be trying to impress YOU.
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Be very comfortable with yourself and who you are. Guys like it when you be yourself. Make conversation with them, as if they were any other friend. Ask them about themselves, and laugh at their jokes/attempts at humor. It's very flirty and it makes them feel good about themselves. Really, though, you shouldn't be trying to impress the guy, the guy should be trying to impress YOU.
Just give him a lovely killing smile