I'll assume everyone reading knows the typical 3-point lighting setup used in cinematography. You have your KEY light which is your main light source, goes on one side of the face, slightly higher than head level. The FILL light which fills in shadows caused by the KEY light, goes on the opposite side and traditionally is about head level. Then finally the HAIR light, used to separate the subject from their background, is behind the subject, typically on the same side as the KEY, higher and spotted down. Below, although crude, I have illustrated my basic 3-point lighting methods using a 3D program. I realize that 3D programs come close but are not exactly 'real world' but hopefully it will illustrate my point sufficiently.
The mistake that many beginners make is that they turn on all of these lights at the same time, then maybe tweak their intensities until they get what they want. Some will get lucky and dial in what they want especially if they know what lighting ratios they usually are after. The key is to turn your lights on one at a time, starting with the KEY and really look to see how it works.
In the following scenario, I have assumed that we are in a 100% dark room for simplicity's sake. That said, let's start with no lights turned on.
Next, let's turn on ONLY the KEY light and see what we get. I have the subject standing right up against a brick wall, which we will talk about soon. But Take a look at what the KEY light does by itself?
See how the left side of our object is well lit but falls off towards the right. This look is more dramatic. Do you like it? Making a NOIR film? Then you're done. 1-point lighting. If your aim isn't to make a NOIR, let's go ahead and add in the FILL light. I have set the FILL's intensity to 50%. Take a look at the difference it makes in the mood.
Now, we can see the pimples on the other side of this actors face. Much better. That said, we still have a nice dramatic falloff between the KEY and FILL side. Have you ever heard someone talk of "Flat lighting"? This isn't it.
Although this looks decent, our actor isn't popping like he should. The background seems to compete a bit with him. Let's fix that by adding a couple of more things. First up, a HAIR Light.
Our lighting setup is complete. However, that dang brick wall background is still competing for screen time with our main actor. It's pretty, and lovely and all but I find that my mind concentrates more on it than him. "And the Oscar goes to..... THE BRICK WALL!". Um. No.
If you can help it, never shoot your subject up against a wall. Your scene needs DEPTH and your focus needs to be clearly on your subject. Let's fix it by moving the actor away from the wall a bit and even opening up our Iris to make our Depth of Field shallower.
Doing the above made the background an 'after thought' and gives our brain a rest so that it can really focus and concentrate on the actor.
In closing, cinematic lighting is all about pushing or pulling the drama using light and dark. Remember, don't be so 'flat' with your Key/Fill ratio. A bit of chiaroscuro is a good thing.