In my work, I very often fake 3D by using 2D tricks like Parallax and re-constructed Z-depth to bring depth of field in the scene.
I thought I'd share a step by step video of How I built the Apollo Lunar Module scene for our short "Forms in Nature: Understanding our Universe"
I use Kevin Dart's PSD files that are layered to optimize the animation. Almost everything meant to be animated has its own layer and is properly named.
I often have to re-build some graphics in After Effects using the shape tool, so the animation process gets more flexible.
I usually start by deciding in my head what I want the action and the camera move to be. And visualize effects and the lighting before I start animating.
It's not a rigide process. Sometimes I just have a vague idea where I'm going when I start. And I let my instinct lead me, keeping in mind that the final look must be faithful to the artist's original design while bringing it to another level of depth and reality. My goal is always to expand people's perception. I want them to feel like we're showing them a portion of something much bigger.