So the night started with me and a buddy just going for a drink and trying to figure out what to do. After extensive texting on both sides of our social circles, we finally managed to find a group of friends going out to town (on a Friday night, who would've figured!). We join up with them, and then make our way to a dorm get-together is what I guess you would call it, it's when all of the tenants of a dormitory join up in the common area for a casual drink, doesn't necessarily have to be a full-blown party.
After a while there, the hostess/organizer (never met her before) starts talking to me, and immediately gets super touchy-feely. Like after telling her that I actually live out of town she said "really?" while energetically rubbing my arm for a few seconds. This kept going on for our whole brief conversation, so I took that as an IOI.
After a while we start talking about getting out of here and hitting the clubs, she says she'g gonna get the rest ready to go (at least 20 people), and goes off to talk to them. I keep on socializing and meeting new people.
When it becomes obvious that everybody of her group was not planning on going out tonight, she leaves with her friend (actually that's a friend we had in common, but I guess she's closer to her. I'll be referring to her as CFriend) to get ready or something. I gather my own group that I came with and start telling them that we need to go. One of mine (Guy) says that he's gonna stay behind and wait for CFriend and the organizer, as he promised to leave with them.
At this point I really wanted to go out and dance, and rationalized that if I stick and wait with him, it may come off as too clingy. In hindsight maybe it wouldn't have been, not sure about that.
After they catch up to us at the club I realize it's just the four of us: me, the hostess, CFriend, and Guy. We all dance in a circle, two guys two girls, but I know that even though CFriend is dating someone, she likes to party. This is where I just stopped pursuing hostess for some reason, maybe escalation anxiety?
While dancing and we'd make eye contact, she'd always smile at me, I always smile back and keep on dancing, but have no idea how to isolate her, and just kind of get anxious imagining just dancing one-on-one. At some point she starts diverting her attention to Guy, and he seems to reciprocate, but they never left the group either. They'd occasionally exchange a few lines but I can't imagine what you would be talking about in a club.
At some point this cool looking muscular dude passes by, he just looks like he's having a good time and I cheer him on, with no hesitation whatsoever we end up dancing in a somewhat suggestive pose (stomach to stomach, intertwined legs, one arm over the other's neck/shoulders) for a few seconds and then get back to our business. I consider myself straight but I always like to joke around with my friends about being gay, and obviously I did not have any problems starting to dance with a random guy, why can't it be the same with a girl that looks like is even into me?

After a while hostess starts seeing a lot of people she knows on the dance floor and kind of drifts away. CFriend is getting hit on by guys left and right, I occasionally "save" her by starting to dance with her in front of the other dude. Guy suddenly starts hating life and is motionlessly standing at the back of the club with a drink in his hand.

I did not get the girl, but I did have fun, dancing is easily my favourite hobby after all. But I still don't know how to use it to approach girls I've met the night before and much less girls I just see on the dance floor.

Seddit-TL;DR: go to a party, organizer kinoes me heavily. Go to a club, become AF-dancing-C instead of escalating/isolating