You meet a new exchange student in your class. How would you ask her what her nationality is?

I would ask her straight up, like "Where do you come from?" or just ask her what her nationality is.

Explanation:

It's better to be straight forward, and not try and work around it, just getting straight to the point is better. Being straightforward stresses the fact that the person will not deviate the conversation from the main focus.

usualmente me lavo los dientes antes de acostarme pero ayer no me lavé.  

usualmente hago mis tareas a las 15: 00pm pero ayer las hice a las 20 pm.  

usualmente llego a mi casa a las siete pero ayer volví a las nueve  

usualmente cocino arroz pero ayer cociné fideos.  

usualmente llamo a mi hermano al mediodía pero ayer lo llamé en la noche