There's this girl I know. Since I'm posting here, you guys can probably guess how I feel about that. We got to know each other through mutual friends, hit it off, et cetera, et cetera. Except! In all of those instances in which we hit it off, it was in a group setting. Lately, we've been getting lunch with each other at least once a week, during which we just... talk.
And that's my problem. Not the talking part, that's pretty great, but the conversations. She tends to dominate the conversation, and I tend to merely listen, and I found that alright until she brought up a point that she didn't like being treated differently, as in, nicer or whatever, by guys that seem to be interested in her. That led me to think as to how I acted around her when we're talking, as opposed to when we're in a group. Generally, I'm much more comfortable and tend to act more bombastic in a group setting while I'm much, much quieter with only her.
And that's because I don't know what to say. I mumble. I stutter. I say things that don't really apply to what she's talking about. So I'm asking the denizens of /love/...
(this also applies as a tl;dr to people who don't really care about my story)
How do you get comfortable talking to a girl one-on-one?