I'm going to disagree here! Corrector - as per PP - should be used first but can be a variety of colours depending on what you want to achieve (reducing redness / lifting a sallow completion etc). It can be combined with a primer (look at the Smashbox website) to reduce the appearence of pores, smooth fine lines etc. Will also help your foundation to 'hold'.
Foundation is then used - evens skin tone, reduces the appearence of pigmentation. Can be tinted moisturiser, full coverage, medium or light coverage, BB cream etc.
Concealer is applied last (in smaller quantities) to cover blemishes and around patches of, say, red skin that's showing through the foundation (around nose for me). You can also use it to reduce the appearence of dark circles under the eyes or you can use a separate light reflective 'pen' here.
If you put concealer on first, you'll 'shift' it when you apply the foundation.
I do concealing last - after eyes, blusher etc - as this allows the foundation to sink in and set, meaning you'll really see where you need extra coverage.
I've spent a lot of time in the company of make up artists and this is what they advise. Also, Google Lisa Eldridge - her website is brilliant for basics and more adventurous looks.