I have been between breathing normally and breathing deep and then releasing the air slowly. I think that one of the mistakes made by so many books regarding this is that they try to break everything down to its parts. Western thinking always seems to mess everything up. They always want to create a formula because we ask for one. Soon the whole thing becomes so complicated that you read two pages of the book and go 'well to hell with this, I didn't know it was so complicated'.
Skilled relaxation is a destination and a journey.
Just like life, we all take different paths. My path may not be exactly like yours and yours not like mine. Like feeling a hair beneath a piece of paper the destination of skilled relaxation is a subtle thing. Point being, find your own breathing. I personally like a few deep breaths at the beginning.