NightClubPhotography
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ISO 400 - 800 range, set camera to M, 1/45, f.4/5.6 for groups.
I would shoot in in Manual, ISO 400, 1/60 at f/5.6 up to f/8 with the flash (bounce if possible, else use a diffuser) providing your primary light.
Try Program mode, Portrait and Night Portrait to see which seems to be best.
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What I do is put the camera on spot meter setting and meter/focus on the face as best I can. THis is particularly useful when the light changes constantly and quickly.