I've had the best luck with not holding the camera tightly at all...rather cradling it as gently as possible such that the inertia of the camera itself is the dominant factor. This works especially well with big cameras. This depends on the camera but most of them will fire shake-free if you dangle them from a string and use the timer. Also my wife with her very petite hands has no trouble shooting my heavier cameras at low speeds. From this I conclude that it's the human factor, mostly the shutter release, that's causing the shake. But then again, I have injured wrists, and gripping tightly will induce a shake in my hands. It plays hell with my shooting; I have to use a rather weak grip and skateboard tape on the grip because gripping firmly will cause shakes to start.