Some times when I take a picture on my iPhone, the force of my finger hitting the snapshot button makes the iPhone move slightly at the last second and cause blur in the picture. To make it much easier to prevent this from happening, just hold your finger down on the camera icon before you steady the iPhone. As long as you keep your finger held down, it won't take the picture. Steady the phone, release your finger from the icon, and the picture will be taken.

This also makes it slightly possible to take a self-portrait. Hold your finger down on the snapshot button, turn the phone around and (try to) aim, then release your finger.