The Rule of Thirds
The rule of thirds is a concept in video and film production in which the frame is divided into into nine imaginary sections, as illustrated on the right. This creates reference points which act as guides for framing the image.
Points (or lines) of interest should occur at 1/3 or 2/3 of the way up (or across) the frame, rather than in the centre. Like many rules of framing, this is not always necessary (or desirable) but it is one of those rules you should understand well before you break it.
In most "people shots", the main line of interest is the line going through the eyes. In this shot, the eyes are placed approximately 1/3 of the way down the frame.
Depending on the type of shot, it's not always possible to place the eyes like this.
In this shot, the building takes up approximately 1/3 of the frame and the sky takes up the rest. This could be a weather shot, in which the subject is actually the sky.