Scriptwriting

What is a script?
Script represents a text document containing a list of instructions that need to be executed by a certain program or scripting manager so that the desired automated action could be achieved. 

What makes an excellent script?

There is a scene heading
The name of the characters, then the dialogue
There is a good of description of action
There is a good of description of diagetic and non-diagetic sound
Good description of Shot- e.g. CUT TO...