Fix the skin weights Using the Component Editor

1.Test the movement of your character by selecting controllers and translating or rotating them around.
2.Determine if joints are affecting the wrong area of geometry

Note:The main areas for shared weights are usually in the legs and feet,the head and shoulder, or the finger.Basically,anywhere when you have parallel areas of geometry and joints.

in this example,the head geomertyis being affected by both the shoulder,arm.wrist joints.so there is a pulling of the geometry.

3.Select the vertices that are being affected incorrectly.

4.Choose Windows>General Editors>Component Editor and click on the Smooth Skin tab

5.in the top list,findthe joints that affecting these points and should not be.Click on the box,then" 0".
in this example,select the row of the head ,then type "1",other row,type"0"

6.repeat this for other affectted areas ,Finish.