The rule of thirds can be used differently for different types of images. For example, for a landscape photo, the horizontal thirds are used, so the horizon can be placed in the top third, the area of interest in the middle third and the foreground in the bottom third.
For images that feature objects as the focal points, the hotspots can be used as your eyes are drawn to these points and this ensures their placement achieves the best effect.
For images or film where people are involved, the vertical thirds can be used. If the person's attention is directed towards the right, it is usually best to place them in the left third and vice-versa.
I have made this video to help explain the rule of thirds using visual examples;
Really bad quality though.
