Through a shed load of trial and error I appear to of got my head around the art of nightclub (or anywhere that is silly amounts of dark and has relatively low ceilings) photography.
The thing that helps me the most is my Samyang 14mm 2.8 lens. The cool thing about the Samyang lenses is they are manual focus. Not like a vintage lens where you have to go backwards and forwards trying to get in focus, but more like you just roughly guess how far away from the subject you are and then change the dial on the lens to how many feet away you are.
So the picture above I was roughly about three foot away from the singer. I had the dial on three foot, walked up to the dude, pointed the camera at him and took the picture.
It would bug the shit out of me having to try and focus on everything that i wanted to take a photo of, especially in a situation where everyone is moving and I was getting paid to get good shots. With the Samyang it's one less thing to worry about.
The second thing I do is bounce the light from the flash on the ceiling. Bounced light is always better. Plus you don't get that annoying on camera flash look to your photos.
Just to give you an idea of my settings. The picture below was at 1/125th of a second at f7.1 and ISO 500.
Hope that helps any photographers that have to do any photography of a nightclub or an event.