The rule of thirds is used to try and identify the four most important parts of an image. I already knew about the rule of thirds due to studying a subject which demanded it back in college. Below is a short video giving a simple explanation for how the rule of thirds is used in film making. Its useful to me because it recommends some tips for where the main focus points should be placed. Especially the point about, when filming of photographing people it's recommended that their eyes are in line with the top two main focus points.