Research: Match On Action

Matching on action refers to a film editing technique where the editor cuts from one shot to another view that matches the first shot's action. Although the two shots may have actually been shot hours apart from each other, cutting on action gives the impression of continuous time when watching the edited film. By having a subject begin an action in one shot and carry it through to completion in the next, the editor creates a visual bridge which distracts the viewer from noticing the cut or noticing any slight continuity error between the two shots.
A variant of cutting on action is a cut in which the subject exits the frame in the first shot and then enters the frame in the subsequent shot. The entrance in the second shot must match the screen direction and motive rhythm of the exit in the first shot.

- Wikipedia

Match On Action is a continuity technique that uses jump-cut editing in order to give the viewer the impression of one continuous take.

It's always important to make sure that action in one take matches in the next, like the speed of a person walking for example.

Also, to keep continuity, if a subject leaves on the right, they must enter on the left, and vice versa.

Here is an example of Match On Action, made by a student.

Research: Shot/Reverse Shot

Shot reverse shot (or shot/countershot) is a film technique where one
character is shown looking at another character (often off-screen), and then the
other character is shown looking back at the first character. Since the
characters are shown facing in opposite directions, the viewer assumes that they
are looking at each other.
-Wikipedia

This is a very common trick in filmmaking. It's used to create a natural flow in a conversation between two characters, like in this clip from the 1942 classic, Casablanca.

Watching a scene of shot/reverse shot, you'd believe that there are actually two cameras shooting the same scene and then the footage is edited in post-production to cut together both piece of film.
However, this isn't so.
Only one camera is used, filming one half of the dialogue and then the second. For example, Character One would act out their lines, followed by a five second pause instead of Character Two's lines. And then vice versa.
A filmmaker may also choose to film reaction shots to put into the scene as further transitions.

+ The scene may be filmed over a course of days
+ Only requires one camera
- Actors must be able to act convincingly against nothing

It's also important to control the location and be able to recreate lighting, otherwise the continuity is lost.

Research: 180 Degree Rule

The 180° rule is a basic guideline in film making that states that two
characters (or other elements) in the same scene should always have the same
left/right relationship to each other. If the camera passes over the imaginary
axis connecting the two subjects, it is called crossing the line. The new shot,
from the opposite side, is known as a reverse angle.
- Wikipedia.

If the 180 degree rule is broken, then the film maker may confuse the viewer, as the characters or subject will have suddenly switched positions.

Here is a video by VideoMaker, illustrating the 180 Degree Rule.