Hey man. Being that I religiously only hit on girls that I am very attracted to (fit, beautiful, nice clothes) then I feel your pain.
These girls can smell you coming a mile off if your game isn't super tight, and when I say that I'm talking about all the subtle behaviours (what your eyes are saying, tone of your voice etc) that you're giving off when approaching and when engaged in conversation, rather than what you're saying or whether she thinks you're a player.

As soon as you go in your head you're finished. These girls get hit on so much that they can spot even the slightest of glitches in your confidence, and 9 times out of 10 they'll just walk off to be with their friends or whatever. All it boils down to really though is you being relaxed and indifferent in your interactions. Getting your inner game sorted out is the most important part, or it was for me personally.

Also, maybe you're being a bit too obvious when you're approaching. With the really hot girls, the more subtle the approach the better in my experience. And by that I don't mean going indirect, I mean make it look like you're not hitting on her to other people, so she doesn't get self conscious in front of everyone in the club, particularly her mates. The way I've found is best to do this is state your interest, eg. you look amazing, and then quickly move the convo on to something non sexual so that you've flipped it from hitting on her to a normal convo. This way she knows that you've got the balls to state why you're stood there talking to her, but there's no pressure on her because you're just having a normal conversation getting to know each other, or whatever. Then obviously after you've built some rapport you start to escalate the situation, which will undoubtedly be met by all kinds of resistance, haha but hey if you want the 9's and 10's you gotta work for it that's for sure.