I'm never really sure about this. On one hand, I don't want to seem so serious and forget to smile. On the other hand, I don't want to feel like I am trying to smile each time I end a sentence. It's sort of like eye contact: when to break it, when to maintain it, etc.

People generally see me as a happy guy. I smile naturally and everything. But the first conversation with a girl is an important window to make an impression. How do I appear warm and inviting without having to smile all the time?