Here is an expression for having a marker trigger a squish and squash. Put the expression on Scale.

In this video tutorial, Eran Stern reveals the first text trick in his series and shows how to design an audio waves animation with the After Effects Text Tool.

This example expression instructs a layer to be at the same position as the next higher layer in the Timeline panel, but delayed by a specified amount of time (in this case, 0.5 seconds). You can set similar expressions for the other geometric properties.

This allows you to control the angle of view of a camera interactively, by scaling a null object
on screen.

This expression will allow you to zoom a camera in After Effects using real-world focal length values.

From Adobe's LiveDocs:

This expression maintains the objects apparent size as it moves away from camera.
It's helpful for taking a flat layout and making a "multiplane" layout from it for animation.

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.