It’s pretty simple and obvious, but I’ve honestly never seen it written down anywhere, so…
Most people taking snapshots or amateur photos — where the subject matter is a person or people — will frame the picture so that the heads are in the vertical center of the photo. It’s perfectly reasonable, given the priority we assign to the head. But it tends to make for unbalanced photos. You often end up with a large empty space in the top half of your frame.
Pull your frame down, before taking the picture, and not only will the image look more natural, but you’ll probably be able to zoom in a little closer, since you’re no longer using only half the frame to try and capture a full person.