Hello again.
I quite often have trouble getting skin tones right in my pictures. A lot of the time, skin comes out with a sort of flat, sickly yellow (or green or blue) cast. Is this just down to lighting and white balance, or can I do anything about it? Is it worth recording a custom white balance? Are there any Rules of Thumb for this issue?
Any info (including any really obvious answers) would be appreciated.

If you are shooting in RAW you can change the White balance in Photoshop RAW options. Also play around with the other options. Also in Photoshop you can adjust tones especially if too much blue/green/yellow hues with colour balance. Image>Adjustments>Colour Balance

Also Hue/Saturation. Where it says edit, teh default will say master, you can change to adjust certain colours.

This may be obvious solution but hope it helps?

If you have a Canon, you may be able to change the color settings themselves and keep your white balance.

Shooting in Jpeg (and really not wanting to shoot in RAW yet), usually using Auto WB (changing occasionally to Flash WB).
Using a Nikon D50 with SB-600.

Take the step up and work in raw, so much more robust to editing. Theres a remove colour cast tool on nikon capture nx that you might like. Or colour balance as Pixifuf said.

Hmm strange.
I've always used Auto WB on jpeg in clubs and found it fine.
Of course get the odd fuck-up here and there where some light source confuses the camera - but they've usually been fine.

One thing I'd say though - before you start messing around with colours - make sure the monitor you're using is displaying them correctly. i.e. Buy, beg, borrow or steal a Screen Calibrator.

for clubbing photos? urgh... there's really no point in my opinion, it's just a waste of space on the card!

AWB should be fine unless the venue/location is really strong in one colour, for instance I once spotted in a venue that was painted red all over the floors, ceiling and walls, so I compensated a little in the WB by making it more blue.

generally though the reason for getting a shot with bad skin colour will be because a coloured light has shone directly onto the subject as you've taken the shot, there's not much you can do about that except take another photo!

Remember that the higher the ISO you're using, the more ambient light you'll pick up and the weaker your flash will fire. If you lower your ISO a bit, you'll get more of the subject lit by just your own light source (the flash) and less of the ambient and club lighting showing up on your subject.

Thanks for all your replies.
I use Capture NX2 as well, and that tool is sometimes really handy.
I have run Adobe Gamma for my screen, and the colours look fairly good on it (when they're right). I have looked into screen calibrators, and will keep an eye on eBay.
Thanks Paul, I'll keep that in mind.

I was crap at using Adobe Gamma.
Relies on you making a judgement - when I first used a calibrator after Gamma - the dark shades were a lot better!

Pauls advice is spot on -
Personally I use Canon and I know there is meant to be a slight difference in the auto wb between the two suppliers - I always set the wb to flash as I feel you can control this a bit better, Pauls point about the ISO is good I rarely ever go higher than 200-400 in clubs.