I have a tablet, but haven't used it at all in skinning (so far).
I just start with some basic shapes with the shape- or pentool and go from there.
Picking up the colours (and mainsponsor) early on is really important as that tends to set some basic rules towards the design.
The tools I've mentioned are the perfect way when you need to fiddle about with complex designs over and around the car. Moving, reshaping etc won't hurt the quality at all.
But then again I've made hundreds of skins and this is just a style I've developed to suit my work. Some other skinner may have developed his/her own style that is just as good for him/her.