I don't have any WIP pix but I assure you, it's pretty easy to do.
It only took me 5-10 minutes to do it.
First I masked off the white part of the sole around the bottom of the shoe,
then I held the shoes at a distance and sprayed it with brown and black.
Make sure you don't get too close, you only want to make them look dirty, you don't want to change the actual color of the shoe.
Then I went back and masked off the big part of the shoe leaving the white sole exposed, and I hit that part lightly with some grey primer. Just enough to make sure it's not so white anymore.
After that I think it's really up to your personal preference. Everyone's shoes look a little different. Some people have scratches and scuffs on the instep of their shoe, and some people have scratches on the outward part.
Maybe you wanna go kicking through the dirt with them too for half a day.