Pick up some books on sculpting. I highly suggest Katherine Dewey's books(link below). Start with her animal book even if you realy want to do people. Animals are easier and faster to learn from. Keep in mind that her lessons may not be the best way to do something but are good ways to teach somebody how to do something.

SculpeyIII is not a very good clay for sculpting and the problems you're having may be due to this. Try out Premo, Kato Polyclay, Super Sculpey or firm super sculpey(my favorite). Each is a little different and only through experimentation will you find one that fits you.

Armatures are very important in sculpting with PC and a toothpick isn't a very good armature. While you may be an amature/beginner/hobbiest you can't expect professional quality if your not using professional quality materials and techniques.

Here's some tutorials. They may not be for things you want to do, but you can get a lot out of them that apply to other subjects.
http://www.conceptart.org/forums/showthread.php?s=d6599cb68807d2eb1da3c4b1411c87b5&threadid=18287&perpage=30&highlight=sculpt&pagenumber=1
http://alterton.iespana.es/needham/2bit.htm
http://www.danperezstudios.com/workshop.htm
Check out the glass attic for more/other polymer clay information.

Vincent Ko Schaefer