I use the same technique as Lordathestrings but I need to adjust my position depending on the guitar I use.

I got a Gibson SG and a Yamaha. With the gibson it's really simple I put the side of my hand directly on the bridge and rotate like Lord says.

On the Yamaha it's different, I can't go real far cause I got a Floyd Rose and if I apply too much pressure I'm changing pitch.

After a while it becomes second nature.