The video posted for hand grip is a good one.
I don't shoot rifles but the concept is you breath while shooting because after running a mile its hard to hold your breath to shoot a rifle. Its better that you learn to regulate your breathing so you don't pass out or or make breathing rhythm eratic as your body's going for air. So applying the same works with a camera. If you had to run up 3 flights of stairs and try to hold your breath you might get one shot off before screwing up your breathing rhythm. But holding your breath while not under physical strain works also.
So this is a YMMV issue, tune your technique to the way you go about getting photos.