The images of your film are the most important technical aspect of production. The camera are the eyes of your audience. And you control them. You decide what your audience is supposed to see and what they're not supposed to see.
The first thing to do is familiarize oneself with certain rules and techniques of camerawork. While there's always a high matter if taste involved in what sort of image people like or dislike - technically spoken, there's quite a range of points where you can divide good and bad camerawork. GOOD camerawork always has a connection to what your current emotional state is. You need to be well aware of what exactly you want to communicate with your shot, then chose what that shoot is supposed to look like.
First, there are obviously different sorts of shots:
EXTREME LONG SHOT
A wide shot that shows a very wide angle, where actors are usually small dots. These shots are commonly used to introduce a location. The viewer is able to get an overview of where he is, what is where. Emotionally, the viewer is distant. He's a spectator. Just watching what happens.
LONG SHOT
The angle is wide, your actor is full in frame, from his feet to his head. And there's a great deal of background visible, but not as much. These shots are commonly used to introduce an actor/object, but still leave details aside. The viewer sees more of the actors/objects and has an overview of them. The location becomes less important, the actor becomes more important. Emotionally, this is a bit closer, but the viewer is still a spectator that gets an overview.
MEDIUM SHOT
This closer shot shows your actors from waist or chest upwards. This is commonly used for all kind of character situations. It's the most used type of shot. You get closer to the actor/object, and the viewer gets more and more drawn into the action/emotion of what's happening. Emotionally, you get more attached.
CLOSE-UP
This focuses on a detail, a face, an object. This is commonly used to draw the attention to something very important. The one ring, the fist of the angry boy, the eyes of the loving woman, the wound of the hurt soldier etc. Emotionally, this is very close. This can be both pleasant or unpleasant, but as a viewer, you're forced to watch a specific detail.
EXTREME CLOSE-UP
This is the closest you can get. Focus on an eye, a mouth, whatever. This is so close, it's very uncommon for the human eye and therefore should be used only in a short sequence where a detail is either very small or you want to attach your audience very close to a character or emotional reaction.
Then we have different types of motion of the camera itself. Theoretically, there's only 3 different sorts of motion you can achieve with your camera:
PANNING
Obviously, you pan from A to B in one shot. Which is your basic tool to show your viewer something, then give him another information later on, by panning to something else/additional. This is different to having both A and B be visible from the beginning. It's a more dosed information control. Control your viewer!
In the example shot, the camera follows the running actor, revealing the mercenaries firing on him in the very last second. This way, the feeling of "running into a trap" has been enforced by the camerawork.
ZOOMING
If you change your zoom throughout a shot, you want your viewer to change his focus. For example, you start in a SUPERCLOSE of an eye, then zoom back up to a CLOSE. You want to start with full emotion, then giving a bit of distance to see what's happening (Could be a shock effect, or whatever). Or the other way round, you start in a TOTAL, then zoom into a CLOSE or even a SUPERCLOSE, you want your viewer to get an overview, then suddenly focus on the eye.
The example video is a scene, where a very slight zoom has been used to draw the viewer closer to the bad guy talking about revenge - this way, we want to make the viewer feel unpleasant by bringing the mencae "closer" to him.
ROLLING
If you move your camera while filming. This gives a different result to just pan or zoom to something else. You force your viewer to change his position. For example in a horror movie, if you move your cam slowly towards the evil creature, you communicate to your viewer, then he can't escape, he's in fact coming closer! Always good in actionsequences too, as it enhances the feeling of "energy".
In the example video, the rolling shot was used to force upon the feeling of threat - as well as enhance the motion of the earlier shot, where the two protagonists are running towards the camera.
The rule of thirds
There's a number of different sets of rules on how to frame a shot. The most commonly referred to is the so called "rule of thirds".
Why exactly the human brain seems to divide images into thirds isn't yet fully clear, but it has been scientifically proven that images that follow those rules are generelly much more pleasantly received.
What you basically do, is divide your shot - no matter what format - into a grid of thirds, like this:
Now you use that grid to place all your objects. The example shot is a close up of police chief willem, looking like this:
And now with the grid of thirds applied:
Now I'll explain why this is - according to the rule of thirds - a pretty much perfectly framed shot:
The matter of attention is the chiefs face. Points of interest in a face are eyes and mouth. As you can see indicated by the yellowish grids, the important part of the frame lies EXACTLY within those two squares. (An other option would be, to have the eyes EXACTLY on the upper horizontal line and the mouth EXACTLY on the lower horizontal line, resulting in a bit closer framed shot).
The middle of the face runs exactly through the first vertical line, again immedieately drawing intereset to it and therefore placing the object "policechief" exactly on that first thirds line.
The blueish grids are left empty (again: 1/3rd of the whole image is left empty for the background. Notice the thirds pattern?). The fact they're on the right side enforces the line of sight of the chief - he's looking to the right of the screen.
Knowing where your actors look is absolutely vital when it comes to the next rule that is often violated in amateur movies:
The "Crossing the Line" rule
This rule is technically very easy, but it's the one that can cause the most headaches. Simply put, the rule goes like this:
In each scene, you have to establish a line of sight for each character (or sometimes even motion of objects) that is NOT ALLOWED TO CHANGE during the scene.
Let's start with the easiest situation: Two people talking to each other:
In the example, you have my character JACK talking to his father, the CRIMELORD. It's the simplest setup. As you can see from the video and the screenshot below, JACK and the CRIMELORD are talking to each other. The line of sight has been established in the first shot: My character Jack is looking to the RIGHT, the crimelord is looking to the left.
So when you combine two shots into one, you see - indicated by the arrows, that these characters are looking at each other. In ALL shots where JACK is visible, he MUST be facing in the same direction whenever he talks to the crimelord. He always has to be facing right and the crimelord always has to be facing left - IF they are supposed to be looking at each other.
This version has the characters NOT looking at each other. Jack is looking at the crimelords back and the crimelord is looking away from his son.
The rules is then broken, when those imaginative arrows don't match to what is supposed to be happening in the scene.
Clever as you are though, you noticed that the line of sight changes in the video above. You can always change the "line", but you need to do it visually. In one shot, my character gets up and walks a few step. In that process, he visibly CROSSES the crimelord and goes to the other side of the image. Now, those eylines are reversed, but must again remain the same in all following shots - until the scene is over or someone crosses someone else.
The rule gets increasingly more difficult with the number of eyelines you have. In the above shot, we have 3 people talking to each other. This shot has the eyelines set to this:
NightCast is looking to the right, whoever he's talking to.
Lynn is looking to the left when talking to NightCast, but to the right when talking to Jerry.
Jerry is looking to the left, whoever he's talking to.
Now, wherever you set up the camera for other shots of the conversation, those line of sights must remain exacty that. So you can't set up any closeup where NightCast would look to the left, or Lynn would be looking to the right talking to him.
As a guide, when setting up shots, you can use this basic idea:
Imagine your actors from the top and draw lines right through them. The camera then can only stay on ONE side of this line. Indicated withe blue area. Both the black camera shots would be valid and remain with the same line of sight. If the camera was placed anywhere in the yellow area, the line would be crossed and the shot invalid.
With three actors however, the placement of the camera is even forther reduced. Placing the camera anywhere in the yellow area would break the rule (because it would change the line of sight of actor number 2).
Now imagine doing a scene with 10 people sitting on a round table...
Another handy piece of advice is is that when you have two characters having a telephone/radio conversation in two different locations and you're cutting between them, it's a good idea to use the same rules as if they were in the same room - this is because it helps the scene flow better, as it establishes the relationship between the two characters.
GENERAL TIPS
Shoot lots of material!
The best idea is to divide your scenes into sequences, then shoot each sequence numerous times using different angles and shot layouts.
Shoot a wide shot from two angles, shoot a closeup from 2 or more angles, shoot a medium shot from 2 or more angles - all through. That way, you are free to do whatever you want in the editing room, because shooting a film and editing it go together.
Only shooting those shots you think you might need is a bad idea, because there can be a whole set of reasons why they might end up not working: Continuity errors, one shot is not usable because you crossed the line, you decide later to change the visual mood of your scene etc.
Make your foreground and background seperable!
Film is a 2D media, so you need to make it easy for the viewer to decode a 3D information of it. Make sure your foreground (usually an actor / actress) is easily seperabla from the background. Either use depth of field (foreground in focus, background not) or make sure the background is noticably darker or brighter then the foreground or has a different color.
Shoot the whole Framing Range!
To make your movie interesting visually, make sure your scenes contain different framing sets. Make sure to actually have Wide shots, closeups, medium shots - the more variety, the better!