good work !
Megawattz gave you really good advises
I'd add perhaps the fact you should try to use green stuff with very little bits at each time. It may seems more difficult, but it's not. It's easier to add putty than remove putty.
Example, when you want to make 2 diferent muscles (refering, for example, to an anatomic book...or even a good marvel comic, or sport magazines, etc...) = use 2 bits of putty.