Raking clay means using a toothed rake (think ribbon tool with grooves) to knock back and scrape away excess clay. I use homemade rakes made from guitar strings and have another made from a jeweler's saw, both made with the wires bent (with heat) and squared off U shape. The tips were inserted into tubing and secured with epoxy. Here's Pete Konig's famous creature tutorial on Concept Art: http://www.conceptart.org/forums/showthread.php?t=18287&page=1&pp=60
From armature to texture all done with SS (Super Sculpey tinted with black and white to make it gray, easier to see flaws). He uses a homemade jeweler's saw rake to help establish the essential forms. It takes a light repetitive touch with a cross hatching stroke to achieve a smooth surface. Follow up with a soft brush and alcohol. 91% works best.
Hope this helps,
Katherine Dewey, aka da frog