Thanks for the answer David.
It's certainly easy to achieve this kind of effect but, for beginners, it can be quite hard to figure out how to do.
Could you share some kind of tutorial ? It would help me improve my process (If I know how a professional create this effect, I can more easily figure out where my errors are). Because at the moment, I try to move sliders and analyse the resulting image...
Well, its probably easier than you think. Start with..
1) Lowering Saturation
2) Lowering contrast (simple way with the slider or being more critical with the Curve tool)
3) Experiment with Output values in the Levels tool, on individual channels. i.e, goto the Blue, channel, pull the TOP slider on the left hand side to give the shadows a cool tone. (You could try with the other channels too)
4) Destaturate certain colours with the colour editor.
Just had a quick play with this shot.. (Attached)