Before you think we're telling you something you already know, hear us out. Most iPhone camera users are aware that tapping the screen will set the point of focus. While this is handy and mostly problem-free, it can get annoying when you move the camera and then have to refocus again. Whether you're trying to capture something that keeps moving, or you just haven't decided on the right angle, continuing to tap the screen to focus can really get in the way.
Now we're going to let you in on the secret: you can lock the camera in focus mode until you have taken your picture. Instead of just tapping the screen, hold for a few seconds until the 'AE/AF Locked' icon appears. Now you can move the camera anywhere and you won't lose focus.