- AI-Servo with AF operation separated from the shutter button. I can achieve "one-shot" focus with a brief press on the AF button, but I also have access to Servo mode the instant I need it. It's one less control to bother about.
- Evaluative metering for now, but thinking about changing to something more precise and predictable, like partial or spot.
- Av, Tv or Manual exposure, but migrating more and more towards manual. When I'm not shooting I leave the camera in "P" mode and 400 ISO so that it's ready for a fast grab shot if something turns up and I have no time to arse around adjusting controls.
- Low speed drive - it's slow enough not to grab an extra shot when you don't mean to, but handy if you want to fire off a burst and don't have time to twiddle controls. I rarely need high speed drive but when I do I'll obviously switch as needed.
- I generally leave WB in daylight setting or a fixed Kelvin value, regardless of conditions. I shoot in raw and I'd rather all my photos started out looking the same, or equally wrong, to begin with rather than having random incorrect WB as the scene before the camera alters. Presets might get you there or thereabouts and could be essential when shooting jpegs but really it's all a bit academic when you shoot raw. I have added "Custom WB" to my favourites menu on my 40D so I may start making the effort to get WB correct in camera. I guess it will help me to get a more accurate RGB histogram for critical exposure analysis. However, I don't actually like my whites to look pure white except in daylight. I quite like a hint of blue on an overcast day and a hint of yellow when shooting in tungsten. I'd rather try to convey that sense of the actual lighting rather than neutralising it to uniform blandness.
- ISO - as low as I can sensibly go without risking camera shake and/or unwanted subject blur.
- Neutral picture style - I don't want my histogram telling me lies because of some artificially manipulated contrast/saturation/sharpening/colour adjustments to the embedded jpeg.
I haven't shot in nightclubs but I imagine evaluative metering will give you a good start but use manual exposure so you are not at the mercy of flashing lights throwing things off all the time. Fire a test shot, check your histogram, adjust and go from there. Manual exposure will also simplify your flash operation too, if you're using flash. As for WB, stick with daylight and then the ambient lighting will show through as it is intended. Shoot raw and you can tweak the WB and recover blown highlights (somewhat) if you need to.