Just try to be calm when you're talking with her. It's natural to feel a little nervous, but if you feel too anxious within your self, then your conversational skills will suffer as a result. And being overly anxious isn't really attractive to women, and they can tell if you are or not. Just try to think of her as someone you've known for a long time.
When making conversation, don't try too hard to think of clever or funny things to say. It'll be obvious that you're trying too hard, and it could come out as too forced or strained. Just say whatever comes naturally, and try not to worry too much if you say something embarassing or weird or whatever. Just keep the conversation flowing. Ask her lots of questions, you know, about her, her interests and hobbies, her work/school, etc, and make sure you listen and show enthusiasm. It should be roughly 65% listening, 35% talking for you.
And I know it's a cliche, but honestly, just be yourself. There's no point pretending to be someone you're not, as firstly, women can tell if you're faking a personality, and secondly, what are you going to do if the date's successful? Just pretend and put on a show whenever you go out with her? Just be yourself, as that way you'll be at your most comfortable and relaxed, and then it'll be easier for the conversation to flow.
Good luck!