Hi @pankaj,
There are a few different ways you can create a facial rig, the simplest one is using goal attachment ( zAttachment with VertexID attribute ):
Another method is by using Rest Shapes:
You need to have sculpts or animation for all the expressions and then plug them to zRestShape ( the same way you do it for blendShape ):
Also to get the most accurate result you need to make full facial muscle rig with fat and skin layers, this workflow is the same with body rig
Hope this helps !