Here is what I am trying to achieve:
I have a video I animated of trees with branches waving "in the wind." I then created floating blue particles with the CC particle generator that also move around. I want these orb particles to appear to be floating around the branches as the tree moves. How could I achieve this? Right now the particles just cover the whole screen.
The first step would be to separate the branches from the background. Put your particles between the background and the branches. Take another copy of your particles and make them a different size and put them on top. Now some particles will move in front of the particles will move behind the branches.
Those are the basics. To make it look believable will take some experimentation.
I remember hearing somewhere that another trick to fake depth is color saturation. In addition to the perception of size being affected by distance, color is as well.