I would think that at a club 50mm might be a bit on the long side if you are shooting from within the action. A Tamron 17-50 2.8 would be a flexible choice. larger 2.8 aperture to help isolate the subjects. I am guessing around f/4 might be ideal, but it depends on where you are standing in relation to the action and what focal length you are at. May not be needed though. I would try with your 18-55 and take it from there.
Some of this may have been mentioned already:
Set the flash to slow-rear sync.
Manual mode, aperture to f/5.6
shutter at 1/30, dial shutter speed up or down to get the effect you're after.
ISO 400-800. Higher ISO will let in more ambient, but may not be needed with shutter speeds at 1/30 or below.
Track with the moving subjects, panning with them as the exposure is taking place. This will take some practice, so I would do a combination of that and standing still shots.
As mentioned, you may want to dial in neg flash compensation, you can do that right on the speedlight.