Run the film through an x-ray machine? Er...
I think it's going to be tough to get the effect that your eyes see. We have the benifit of taking it all in in 3D. We can see that it gets thicker as you get deeper, but on film, it tends to just turn out as a haze.
I haven't worked with it much, but if you want to do fog, you might keep your eye out for when there is a distinct gradient or cut-off, like when it looks like a cloud is taking up the first few feet off the gound and maybe has some whisps coming up off of it, but is somewhat clear above. I would guess that a long telephoto could help also. Since it compresses distance, you would probably notice a greater distinction of the fog, but you'd have to include subject matter over a range of distances. But then a wide-angle would allow you to easily have something close and unaffected in the foreground. I guess it would depend on conditions, but that's something you can experiment with. I'm guessing a thick fog = wide-angle and thin haze = telephoto.