Get some fairly stiff wire(And relatively thick).
You can make a few armatures at the same time, if you intend to always work in the same scale. If you are working in 1/6, scale the armatures to a GI Joe 12" figure, and then you can alter it from there on if the figure is taller or shorter slightly(And you can also alter the pose easily).
You need strong wire, so that you should need a set of pliers to work it. This gives it strength when you have it in the desired shape.
And don't worry if you can only get short lengths of wire. If it's strong enough, you can always wrap two pieces with electrical wire, and solder it together.
After you have the wire armature done, get some cheap aluminium foil, cut it into smallish squares and(Piece by piece, in layers), wrap the armature with this. The reason for this is two-fold:
1. It helps to "cook" the Sculpey(Or equivalent) from the inside out(Because aluminium foil is such a great insulator), and:
2. It builds the armature up to almost the shape of the figure to be sculpted, and so it saves on clay.
I hope this helps.
Bar.
:lol
