Today i was working on some deformation using an older parallel blender blendshape way but the issue as Jakub Krompoic points out on Matt Estela's rigging blog on (Corrective blendshapes without PSDs), was that when i rotate a parent joint of the joint driving corrective the correctives started to mess up. So i began learning Michael Comet's pose deformer tool.
Comet's pose deformer tool is spectacular. It is able to read joint poses and then let you sculpt a correction and it takes care of all the math stuff. If your sculpting corrective in ZBrush make sure to use GoZ because it helps maintain the same scale of the character leaving and coming back into Maya.
I also highly recommend checking out Carlos Sansonetti's amazing "The Skinned Character Rig". He goes into detail of lots of cool skinning workflows. He also gives a detailed description of how to use Comet tools.
Also for some great rigging reference check out the "Movements of the Upper Limb" Anatomy Modules on University of Michigan Medical school website (med.umich.edu) click on the top right button above home to see the movements.
Happy rigging and sculpting,
Michael Comet (www dot comet-cartoons dot com)
Carlos Sansonetti (carlosansonetti dot com)
Matt Estela (www dot tokeru dot com)
Jakub Krompoic (syntetik dot blogspot dot com)