It all starts with the photography and the vision. Normally the request comes in from an art director, typically they request a dynamic shot that shows the technology and the product in the best light.
In this image, the goal was to get a great look at the shoe and to plant the shoe in the image as a whole. The image should be nearly ready to go out the door right out of the camera. This shoe was hung above the scene and lit for a single capture. All hanging supports were removed in Photoshop.
I go over the image and add a bace level of effects to get the ball rolling. Since I build the image in my head before starting the project, the first pass is my proof of concept. If my idea isn't going to work I'll know durning this initial effects composite.
For this shot I added volume, particals and atmosphere. You'll also notice a flare from the top right, the shoe was lit so that the flare could be added in post.
The second time through the image more atmosphere and particles are added. Every thing in this image besides the original image is rendered. In later passes i'll add real dirt to add a little to the realism.
Second Draft-Additional Environment
This image is the scene minus the shoe. This gives an idea of how the scene works on its own.