Rules of Concealment: How do you do yours?

Concealer's a tricksy business, isn't it? Trying to find one that'll zap yer zits, mask redness and camouflage the tell-tale signs you had 90 scoops last night is not an easy task, but if you do manage it, then you've got the thorny question of the order in which you're meant to apply it to deal with.

Makeup maven Bobbi Brown insists it should be done first, as that way she reckons you use less foundation and achieve a more natural look.  It makes sense, sure. I understand the rationale and nodded along when it was explained to me.

But lots of other makeup artists conceal second after applying foundation and I have to say, this is generally what I do too, unless it's very warm and I know foundation will slide off in about two seconds flat.  The idea behind the do-it-after approach is that your base makeup will probably take care of the majority of what you want to cover, and anything that needs a more heavy-duty hand - like dark circles - can be addressed last.

What do you do, though? Lets rate our concealer preferences in the comments!