Enveloping (skinning) tips

> use the default values for the envelope (2 skeleton objects and distance based);
> apply a smooth (leave the default values);
> animate or move deformers to see where the weighting needs to be improved;
> sometimes it will be easier to select the points and reassign locally to the deformers they should be assigned to;
> painting weights works well for large area revisions but is a bit difficult to control the accuracy for smaller areas;
> for the final tweaks you may need to edit individual point weighting, selecting a bone with the weight editor open and scrolling through each point works well (although a bit tedious);
> when you are happy with the enveloping, freeze the envelope modifications and save a preset (from the Envelope_Weight property page, located under the Clusters > EnvelopeWeightCls);
> make sure to occasionally check a render region while you are enveloping, or render a short animation sequence, creases in the skinning may be seen in a mental ray render that you don't see in hidden line or shaded.

If you need to add a bone or other deformer to the rig / or if you need to add points to the geometry:
> save a preset of the envelope weights;
> return to the default skeleton pose;
> mute the envelope;
> add the deformer or the points to the geometry;
> set the envelope (leave "automatically reassign envelope" toggled off);
> turn the envelope back on;
> load the preset;
> reassign the points near the added deformer as necessary or in the case of adding points to the geometry reassign the newly added points to the nearest deformers.