I think I have clayed about 100 cars (Im not a detailing guy anyway), my usual clay bar is the blue one (I think its called medium) and I usually would have a 1 kg brick of it which I would slice into about 16 small ones - reason for brick was that it would somehow vanish and my freind's cars would be smooth n shiny and that it was good money too.
mix up some car shampoo and clay away. its easy - yes you need to use common sense like - Dont use it on hot body surface or dusty environment or reuse it after dropping, or use it with long strokes (anyone who has painted a car knows this)
I cannot think of any other "technicality to claying"
I did however see a car once in Karachi whose owner had bought some clay magic (the original) from "vilayat" - his car - a civic of some sort with the necessary neons, stickers, exhaust box etc. - The guy removed the clay from the box but could not see that it was tightly wrapped in cellophane, he rubbed his car with it - lol.