Hey there buddy!
as promised - a quick environ line
I do agree with Stace! A good way to get some depth into your environ is to use those three "levels". For that - keep in mind that the closest elements are the darkest (as closer the element will be to the cam, as darker it gets). Another good way is to use some customized brushes and shape for the structure and textures. Do you work with something like that? maybe I could share some of my brushes and shapes with you. Just let me know.
And - just in case you're interested - I did some screen caps and tutorials for landscape/environs. They are on my blog. Maybe they will be a bit more helpfull than my poor english.
If you have any questions - just drop me a line and I'll get back to you asap. Or we could do a collab.