The 180 Degree Rule is a basic filmmaker guideline on the on-screen positioning of the characters in the scene. There is an imaginary line, called the axis, this is where the actors would stand. By doing this, no matter where the camera is on that arc, the first character will always be frame right of the second character. This is important for the film maker because they can then portray different sides of a story in the same scene. An example of this is Peter Jacksons Lord of the Rings films, where Gollum has a conversation with himself. The use of the 180 degree rule in this scene helps the director show Gollums different characteristics, so when he is playing the good Gollum he faces left, and when he is the bad gollum he faces right.
Rule of Thirds is where there is a 3 x 3 grid over an image. This has 9 equal squares which help to place the certain aspects of the image. For example, in a scene where two characters are speaking, they don't necessarily have to be in the same take as each other. What the film maker would do is film the characters at different times, but have on on the far side of the left grid, and the other on the far side of the right grid. On the right is a landscape shot of a tree. The grid shows how the camera has taken the image and made the tree and the other main parts of the image fit into the 9 squares. The significance of using the Rule of Thirds is really shown when it comes to close ups of someones face. When taking a close up shot of a face, people use the rule of thirds to make sure that the face is proportionate to the shot, and that certain facial features are in the right part of the grid. For example, someones nose would normally be within the centre of the grid, and if that is the case then the shot is most likely centre.