As a director, you should begin planning what you're going to do when you get to the set long before the shooting starts. Whether or not you're working from a script, you should develop a shot list to ensure that whatever the subject you're filming, you'll get enough coverage to successfully edit the scene.
Coverage refers to the collection of shots you will film to tell the story of the scene. You might get some wide shots and some close-ups, and various other shots so that in the editing room, you'll have many options to ensure the story is communicated in the most effective way possible.
The process of planning what shots you will shoot is known as previsualization and it can take many forms, from a simple list of shots to comic-book like storyboards that show each camera angle as a still picture; to loosely arranged animations of those still images timed to an audio reading of the script (called an animatic) to full-on 3D renderings of the scene with all the planned edits already worked out.
To keep things simple, I'm going to start with the simplest form of previsualization, which is just making a simple list of the shots you think will be necessary to cover the scene. And for starters let's assume we're working in a narrative scenario: Let's take a simple domestic scene of a woman coming home and sitting down to dinner with her husband.
In this scene, the woman comes home, greets her husband who has been waiting for her, then goes into the kitchen and grabs a glass of wine, the two speak for a moment in the kitchen doorway, then they move into the dining room, and finally they sit down.
When you plan how you're going to cover any particular scene, you ought to have some idea of how it might be edited, but you should never limit yourself to just one exact editing sequence. You never know what issues might arise based on technical limitations, performance, or the timing of the finished scene. It's essential that you always provide enough coverage so your editor will have many cutting options.
The first shot you should always think about is the Master shot. A master shot is a shot that contains all of the action in the scene. So you'll want to find an angle on the event where your camera can record everything that happens in that scene.
Usually Master shots are wide shots, simply because a wider frame allows you to see all the action that will occur. However, there's no rule that a master has to be wide (or static, for that matter) But you do want to shoot the master from a camera angle that isn't obscured by a wall or another object, and isn't so wide that you can't see what's going on, and isn't so compromised that the editor won't want to use it.
Even though a master shot captures all of the action in a scene, it almost certainly won't be used for the duration of the scene. Because it's (usually) so wide, you're going to likely want to cut into closer angles to capture the emotional meat of the scene.
So, in addition to the Master, you'll want to get coverage (sometimes coverage refers to shots in addition to the master). Typically for a two-person scene, that means a pair of matching medium close-ups (MCUs), usually over-the-shoulder (OTS) shots, and a pair of close-ups (CUs).
That's the bare minimum; five shots:
Over the Shoulder 1
Over the Shoulder 2
With those five shots, you can probably safely edit the scene well enough.
We call that standard coverage.
If there's a lot of movement in a scene and you can't cover it all in one master, you can shoot separate masters (and corresponding coverage) for the different parts of the scene.
So, for example, if there's part of the scene where they're sitting at the dining table and part of the scene where they're standing in the doorway, even though it's technically one scene, you'll need to treat it like multiple scenes, each with its own set of coverage:
Now, you may think it's super boring to always use these same five shots for every scene, but guess what? It works.
Take a look at any movie or TV show and you'll see this sequence of shots used over and over and over again.
Of course there are thousands of ways to make these basics unique, which we'll talk about in great detail, and there are lots of other shots you should be getting in addition, but start with these five and you're most of the way to having captured the scene at hand.
Standard coverage is only the bare minimum of the shots you should get for each scene. To learn about what other shots you should add to your shot list when planning each scene, see the Film Craft 103: The Director course.