Find interesting topics to talk about and crack a joke here and there. The more laid back you are, and just treating her as your good friend allows you to be comfortable to be yourself and talk about anything and everything that is not just about you. Crack a joke in between to let her know of your funny side as well. (Google)
If you crack a joke in the middle of a serious moment, from then on, you will be seen as a joker. (Google)