It really depends on your area, the locals, and the club itself.
In my area, I've seen everything from mall-goth to full on latex body-suits and hoods. It depends on the focus of the club, the events going on, and stuff. I've even seen random people in preppy clothing who don't seem to notice or care where they are.
If the place has a website, you can check their info and if they have any dress-code regulations (some places they may or may not allow people to be topless or bring oversize accessories, stuff like that), and look at pictures to see what the atmosphere is like.