This is from an older version but it should be relevant, I hope...
1. When applying Smooth Skin go into the options and choose settings that fits your geometry/joints. For example you might want the the weight distribution be set to "joint hierarchie" or to the "closest joint". This effects how good the initial skin weight is performed by Maya. Also you might want to choose only "3" joints, participating in weighting instead of the default "5". You can also choose to lock that number, so that Maya doesn't try to add weights to more joints, while painting them. Because Maya will allways try to get a skin weight value of 1 for each vertex of your geometry, unless you uncheck a feature called... umm forgot its name... anyway...

2. While painting skin weights, try to stay away from "smooth" painting. Always try to "Add" skin weight values as much as possible.

3. "Lock skin weights" on all but neighboring 2 or 3 joints while painting skin weights. That way a joint on the other end of your joint hierarchy doesn't get assigned unwanted skin weight values.

4. Use the "component editor" for larger areas of your geometry, that will get the same value. Remember to "lock skin weights" on all but the joints you want to be affected.

5. Use "Prune small weights" with an appropriate value.
That will help to get rid of small skin weight values of unwanted joints.

6. If you like to, set your workspace background color to black
in order to better see where you paint weights in white color.