Watch out for that man clipping the hedge – especially if he raises his head with a meaning look. He’s a detective, a spy, a goon or someone planted to act as your bodyguard.
A man is sitting at a desk, apparently asleep. You tap him on the shoulder – he slumps to the floor, dead. OR he is sitting in his swivel office chair facing the window. You put your hand on the chair – it swivels round to face you revealing the occupant slumped on the seat, dead.
A character addresses the camera: “Why, I didn’t expect to find YOU here! Now, there’s plenty for both of us – why don’t we just divvy it up and go home?” We see other person’s gloved hand with gun in it. He/she shoots, first person falls dead.
First law of TV drama: if a woman talks to a man about "us", the relationship is doomed/over/never existed outside her own head.
Blind beggar sees all through dark glasses. Person in wheelchair can really walk.
In night street scenes, the streets are always wet. (Apparently deliberately wetted so they reflect the light.)
When someone is buried at sea, the one black character will recite Psalm 23.
In bad period drama an older woman will constantly address a younger one as “child”.
Herds of dinosaurs are always setting off on a doomed trek into a desert as the rivers dry up.
More here, here and here.