As well as writing for the stage you could write a script for radio, TV or film/video.
Much of what has been said will also apply if you are writing a script for a medium other than the stage. However there are important differences.
In media other than stage drama you do not need to worry about whether or not you can stage the plot. In radio you can write about almost anything you can imagine. In TV and film you need to think about the visual impact of what you're writing.
There are also techniques specific to the different media, which will replace or add to the stage directions.
On stage the audience's viewpoint is fairly static. In film or TV we see things through the eye of the camera. You need to write down what you want the camera to be looking at while the dialogue is spoken. Do you want it to look at one character in close up? Do you want it to move around the room? You need to specify this in your directions.
The main things you need to consider are sound effects. The listener cannot see anything so you need to suggest what is happening by sound. These could be sounds like:
Sound effects should be in brackets like stage directions.