A prime wide angle, normal or short telephoto lens with a large aperture (in descending order) of .095,1.2 or1.4 would be good.
You would be using lens wide open or one stop closed. And you need to focus or pre-focus on a spot to make usable images.
You would need a slow hand holdable shutter speed of at least 1/30 second to make a usable image. And you would need to touch off the shutter just as the action stops momentarily and not when subject is in motion as you will get a blurred image.
As for iso. 400 would work for like usual room lighting. For unknown low lighting conditions, a higher iso number setting is recommended. I would start with taking pics at iso 1600. Then move it up to 3200 and possibly higher...6200 and maybe more if your camera iso settings will get that high.
You must place yourself to be at a place with the most reflected light or where you will use light to compose your image.
And you would be wasting your time, I believe, trying to use zoom style lenses with smaller apertures. These are great for most lighting conditions, but not suitable for low light work.
1) you wouldn't be using ISO400 in a nightclub... you'd need to be using a LOT higher!!!
2) lens would depend on your proximity to the "action" - 50mm 35mm (f/1.4) or a wide angle...