Computersight -

1) First grab a photo of anything.

2) Go To Layers –> Adjustments –> Channel Mixer

This will change the colors in the selected layer, generally all you have to do is play around with the Blue and Green channel, keep the Red how it is unless you can make it look better. You want to make the layer a bit darker and mysterious.

3) Now you want to make the mist.

Create a new layer and use the fill tool on the empty layer. Then make the layer slightly red, make sure that the opacity is roughly 10%-40%. You should have something like this:

Its now slightly darker.

4) Add Clouds

Create New Layer –> Images –> Adjustments –> Render –> Clouds
Then just select parts of the clouds and using the channel mixer create a deadly mist like this.

Good Luck