If a girl you have just met asks "what do you do?" , you've fucked up. It's a sign she's either bored or you've failed to get into rapport (or both).
"What do you do?" is the question people ask when they feel awkward with a new person, need to fill a gap, and can't think of anything else to say.
You need to work on your conversation skillz, brah.
By the time you get to this question, you should already know enough about her to frame your answer perfectly. For example:
How educated is she?
Who does she work for? (if she's not at college)
Does she have dreams of working for herself one day?
Is that want she wants to do with her life?
If not, why hasn't she done it already?
Is she more of an arts or science person?
Once you have that information, you can shape your answers much better. That way you can build lots of little points of connection where it sounds like you've got loads in common with her.
The problem with giving "smart", prepared answers like I'm a lion tamer or some shit like that is unless you carry it off perfectly, it screams "I've read a book on how to be suck-cessful with women."