In the case of this collage, I have brought the deer more forward in the collage by placing the foam sticky squares behind the graphic of the deer while much of the greenery surrounding the deer is more in the background.
I often place some foam squares on parts of the foliage but not all of it. For example, I might glue the base of the leaf to the background but place 1-2 foam squares at the outer end of the leaf to lift it forward. That helps me create some depth as well as a sense of movement in the layers of the collage.
Notice that I have also embedded some torn sari silk among the layers to add color and texture to the piece.
Graphic images came from The Graphics Fairy. https://members.thegraphicsfairy.com/category/bundles/
This page is from my "Nurturing Nature" visual storybook which can be seen on my Instagram page https://www.instagram.com/august_birdsong/?hl=en .
The video of the storybook can be seen on The Graphics Fairy's YT channel at https://www.youtube.com/watch?v=-lSRLk60aAs&t=1300s. 