Firstly, you don't really want to actually ask a girl to dance, you want to use eye contact and body language to just start dancing with her
as for how good Nightclubs are for picking up girls, they are obviously great places, many many girls go home with guys for sex from nightclubs
You are either a club guy or you aren't. No shame if you aren't.
Generally you do need to be somewhat attractive and well dressed, having status definitely helps as well.
A fat ugly guy generally aint pulling from a nightclub, it is a superficial environment
The one key to nightgame is to get a girl to act like a slut without feeling like a slut.
These is so much easier in holiday destinations which is why girls on holiday are so much easier to pull. In their home city, girls are so worried about looking like a slut to their social circle.
Not all clubs are sausage fests. You need to know where to go and when
Right club at the right time, you are going to see a ton of hot girls in the same place that you just won't see during the day. If you know your city's club scene well, you can get clubs full of model types.
If your not a nightlife type of person, don't do it, do daygame