picking technique

Hi David,

I've been playing with a pick now for 2 years but I think I haven't developed a good technique. Sometimes when we play live, my hand starts to cramp from holding the pick too firmly and if I loosen my grip, the pick starts sliding out of position. I really love the way Justin Chancellor sounds with his pick. Do know his technique? He's got a really solid thump to his playing that I need. Sometimes my picking can sound thin and just plain awful.

Also when you pick do you move your wrist? or your forearm?
our bands guitarist tells me to play from the forearm but it seems really unnatural.

Thanks,

Tony