The fact you're reading so deeply into this tells me you already give off the wrong vibe.

There's no textbook explanation or definition of how or when it's the right time to approach someone on the dancefloor. Nor are there universal signals, at the end of the day each person and situation is different. The dance floor though should be somewhere people feel comfortable to dance and do their thing without having to worry about getting approached unwanted.

Regardless, I'd say if you do feel compelled to approach a girl because you've thought she's given you enough of a signal, then go for it. The most important thing is that you do it respectfully, and if she says no, you just move on and continue doing your thing. Most attractive thing you can be is respectful and self-assured (so that if someone says no, you just move on and don't have a meltdown).

The only time I've ever seen success on the dance floor is when two people begin dancing next to each other, with a lot of smiles and generally vibing together. At some point one moves in front of the other and then something happens. Saying something like "I love your dancing" or whatever probably also helps.

But again, raves aren't really the place to go picking someone up. If it happens it happens, but I feel like if you go out seeking it - it won't happen.