Premiumbeat has put up a tutorial on how to use wiggle expressions to add random movements to your animations in Adobe After Effects:
Wiggle is one of the more versatile After Effects expressions. You can apply it to a layer in your AE project to add movement to position, rotation and scale. By modifying the parameters in the expression you can set limits on the magnitude and frequency of the animation.
The video tutorial below, by motion designer Jens Uttikal, provides a nice overall tutorial on the capabilities of Wiggle and how to integrate it into your After Effects project. It’s a worthwhile 6 minute viewing for all AE users.