Free Floating vs Parented Joints
How the joints are parented in the hierarchy can affect the initial bind results when a skin is applied. Below you'll see two examples; one is the result of the joints being parented to each other, the other is if they are left free floating (Fig.11).
Fig. 11 - Default skin weights: hierarchy joints vs free floating
Twist joints help maintain volume when the joint chain is twisted along the primary axis. The most common example of this is the forearm twist. As the hand rotates, the volume in the forearm will be lost if weighed to the wrist joint, or left to sheer if not influenced at all (Fig.12).
Fig. 12 - Twist joints maintain volume
Adding in these additional joints spreads out the distribution of the rotation value along the entire chain. Not only is the rotational value spread, but also helps the position of the verts being weighed, though that is slightly more difficult to explain.
You can learn more about setups and solutions for overcoming forearm and other twist areas in a previous write-up: http://www.3dfiggins.com/writeups/forearmTwist/
You can add additional joints to a skin that can help preserve specific volumes. These joints can be directly animated by hand for spot fixes, driven by Set Driven Keys or nodes for automation.
One key place to have additional joints is the shoulder. A great example can be seen in this tutorial/script by Peter Shipkov: http://petershipkov.com/development/shoulderrig/shoulderrig.htm
Another area is the elbow/knee. By placing two more joints in the skin for the front and back of the bend joint, you can have them push away as the limb bends. In turn, this will pull out the verts and give just a bit more volume in the crease area (Fig.13).
Fig. 13 - Extra joints to push out on elbows
How to Weight Multiple/Dense/Overlapping Meshes
Sock puppet skinning is based off merging overlapping meshes and removing unnecessary polygons to make a clean, single mesh to paint weights on to later transfer those weights back to the original meshes.
This process can be used in multiple instances, and can help speed up rigging facets (Fig.14 - 15).
Fig. 14 - Low res cage for facial meshes
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Fig. 15 - Low res cage for complex/multiple meshes