Regularly to add depth, use the Burn Tool to darken light spots and the dodge tool to lighten overdarkened spots.
There is an automatic-depth-adder-thing that can help you add depth with simplicity.
It goes as follows, and be sure you are familiar with the Photoshop Interface.
Once you are finished with your work follow these steps:
1. Filter > Other > High Pass
2. 10.0 on the High Pass setting
3. Set that layer on Overlay or Soft Light, your choice.
This should put a nice tone to your work instantaneously, just like C4D's would.