I watched a few of the videos from the Character Rigging for Production in Maya tutorial series on DigitalTutors.
Techniques
1. We can use curves and shapes as handles for joints, rather than moving the joints themselves. This allows for a separation of controls and the underlying rig structure.
Video: Building Facial Controls
2. Building on the previous technique, you can create nested layers of handles. For example, creating a curve to use as a general eyebrow handle that is the parent of the three handles that control the eyebrow shape.
3. It is possible to create dynamic parenting relationships, so that you can choose whether or not a parent object affects the transformation of the child, all using a slider or other dynamic control. (Note the Follow attribute that is highlighted in the Channel Box/Layer Editor.)
