Show don’t tell.
People pay lip service to this concept but as far as I can see, it’s truly understood by only about one per cent of writers. You can have a scene between two people who never say an unkind word to each other
and yet make it clear that they hate each other’s guts. That’s what it’s all about, and yet you often see scripts —or even finished programmes— where there is no subtext at all, where everything is written all over the screen in day-glo colours, for fear that someone might miss the intention.
I sometimes do rewrite work and that is all I have to do: Take all the telling and turn it into showing. It’s a laughably simple concept and yet constantly overlooked.