How do I stop being so awkward around people I don't know well?

Im visiting my brother and his girlfriend. I came with a few friends that I've known for a long time who im very comfortable around. My brothers girlfriend invited one of her friends. At first it wasn't too bad, but we kind of ran out of things to talk about. Im honestly kind of a quiet guy as it is, but I could tell she was trying to start conversations with me, but id give sort of short responses. I just didn't know what to say. Mostly because I was afraid to be myself around her in fear of looking like a fool. My brother is kind of like me, but he kept talking. I don't know what my problem is.

How do I stop being so awkward around people I don't know well?
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