What questions to ask to keep the mood fun?

To keep the mood fun, ask questions about things which the person is interested in. For example, if they love watching pretty little liars, ask them who they think a is (bad example, sorry :P). If you don't know about their interests, ask them- e.g. 'whats your favourite tv show?'. Maybe you could crack a couple of jokes. Just always make sure you are kind, and are not rude or nosy, then you can keep the mood fun :)