How should characters enter and exit the frame?
When filming a scene where the subject is walking in/out of the frame, it is essential that the character enters and exit the frame in the same direction. For example, if there are two shots of a man walking from one house to another, and the man enters the shot on the right and exits in the left in the first shot, the man should enter on the right and exit the left in the second shot as well.
What happens if these “rules” are not followed?
Not following this idea can confuse your audience into thinking that the subject sharply changed direction in between shots.
How does this apply to diagonal movement in the frame?
The same rules of entering and exiting the frame apply to diagonal movement. If the subject enters the screen diagonally on the right and exits towards the left, the following scene should also follow this direction, whether it is also diagonal or straight.
Another thing to keep in mind with diagonal shots is the size of the subject between two shots. If there is a cut from when the subject is very close to the camera to when they’re far away, and small, this imbalance of size will not look good to an audience, and they may feel the continuity has been disrupted.
Instead, try to cut when the character appears to be about the same size as they are in the head of the next shot.