If you're really listening to your partner, even if that's the casting director, you're going to have a better audition. You can use what they are giving you to color what you're doing and re-act what they're giving you.
Acting/re-acting, you know that one right? If not, don't worry, it's coming.
"But they're not giving me anything!" you say. Great. Make it about them not giving you anything. If the scene calls for some kind of desperation, anger, or resentment, that makes it all the more easy to use that lack of giving. Deliver the line as if you really want that person to hear & understand you.
If they are giving you a little bit, run with that shit. They're trying to help. They'll be the first to tell you they're not actors, but that doesn't mean they're not trying to help you out from time to time.
Also, listen to what they give you for notes.
So many times, casting will say. That was good, now can you do it more angry/sad/confident/whatever. Really listen and see if you can get a feel for what they're going for. Most of the time, they want to see something different, to see if you're directable, or if you've just rehearsed the shit out of it, and are now stuck in a rut.
Be open to change, and listen.