How to make the girl I date open her self ? it seems all my question is answered not seriously?

every time I date with this girl I have bad conversation. i don't know what to talk about. and every time I ask her anything she won't answer seriously. how can I make her open up and answer seriously?|||maybe thats how she is when she's nervous, I laugh and joke a lot when I'm nervous, and maybe it makes her more nervous if the conversation isnt flowing and you get that awkward silence