Some great After Effects tutorials coming from Ryan Boyle and in this one, Ryan shows how to create expressions for a Puppet Pin in After Effects to the X and Y positions separately when using the After Effects puppet tool for character animation.
Ryan Boyle writes: This tutorial covers how to apply expressions to the x and y positions separately in the puppet tool. In the previous tutorial, Wiggle on Position, I showed you how to apply a wiggle position to x and y separately using the Separate Dimensions option. The puppet tool in After Effects doesn’t have this option so we have to use an expression to achieve the same effect.
In this tutorial we use the following expression:
Wiggle (5,10) means wiggle 5 times a second 10 pixels. In After Effects  is the x position,  is the y position, and  is the z position. When you use the “value” expression it keeps the value editable and doesn’t effect or break the expression if you change it.