Agree with both Atom Smasher and Barrister on this. The way I do it is to not be impressed by her until she has earned it, and to make her qualify herself by questioning her on something she says - sometimes in a slightly critical way. On the first point, what I mean is that many guys will have an interaction like this:
Him: "So, what do you like to do for fun?"
Her: "I like to go out for brunch with my friends"
Him "OH WOW! THAT IS SO COOL!!!!! I LOVE BRUNCH!!!" (I'm obviously laying it on thick here but you get the idea, and many guys do this)
Instead I might say, "I see - well, you're certainly doing your part to reinforce the stereotype. Do you also love Starbucks and Panera bread?" and I would say this with a sh*t eating grin. This example is toward the harsher end of the spectrum. A less harsh example would be to just stare at her blankly and not say anything and sit there in silence until she says something. And a slightly less harsh example would be to say something like, "Ah, that's it?" in an unimpressed tone. Also Atom Smasher's example of saying she lost some points is perfect too. All of these things will shift the power dynamic like Atom Smasher said, and will have her beginning to qualify herself to you.
Now if and when she says something truly deserving of recognition and being impressed, your eyes can light up and you can reward her for that by saying it's cool/impressive/whatever. The point is, you only do it where it's earned and you aren't afraid of expressing disappointment. This makes women incredibly turned on. 98% of guys don't do this.