After Effects Camera Mapping Tutorial 2D to 3D

Interactively control camera focus distance.
The camera will focus wherever your null or solid happens to sit. This expression is golden when you're doing a lot of Depth of Field work.

Apply this expression to the opacity attribute and it'll disappear whenever it's flipped away from the camera. You need to have an active camera in your composition for this one to work.

Apply this expression to your 'Scale' attribute and it'll automatically 'flip' the layer in 3d space when the camera goes behind it. This way, your text will never be seen from behind, for instance.