You're bumping the clarity down WAY too much! It's so obvious
Unless it's your style (what you were aiming for), I respect your artistic choice!
I know girls love their shots with the clarity bumped down because it eliminates any problems in the skin... but you should remove it yourself so the rest of the picture has more clarity.
Here's an example of a shot I took: https://fbcdn-sphotos-e-a.akamaihd.n...32342267_n.jpg
I removed her skin defects using Lightroom, and bumped the clarity up a bit so you can see the detail in her cosplay.
For convention shoots I find that lying on the ground and aiming towards the sky is a good way to eliminate the "con" background. I see that you have one shot like that! The highlights aka sky are blown out though, and that's because your camera is trying to expose for your subject. If you have just one flash, you can try to expose for the sky and let the flash fill your subject, your shots will look much better that way.
Are you coming to Otakuthon? By the way what kind of lens do you use?