You'd also do well to form a thicker piece to make it easier to hold and use.
Dayum, that's a big piece of clay.
More lube!
Now Keg, be careful with that, you shouldn't be pointing out to him a proper wash and decontamination stage would have removed the majority of that dirt before clay touched it
I didn't look through the replies to start with, then went back in to see if anyone had asked the question. I want to but I can imagine the response.
Use a watery shampoo mix or quick detailed sprayed over part of the panel you're working the clay over. That way you're not rubbing dirt imbedded in the clay back over the panel, and will stop it from sticking or catching on the paint. As said keep refolding the clay to create a clean face, once it's all pretty dirty discard and use a clean peace
Typically a good wash, tar remover and then iron remover will cut a lot of the dirt you pick up from claying, then keep it sealed or waxed to cut down on further bonded contaminants in the future
Wow. Tbf it could look like this... http://www.detailingworld.co.uk/forum/showthread.php?t=278206
Now explained! Hummmmmmm.