Speaking of conventions in movies (I mentioned a starving person seeing someone turned into a chicken in my post on Charlie Chaplin), Television Tropes, Idioms, and Devices catalogues all of the commonly-used devices in TV shows. An example:

Door Focus

When a character leaves a room and the focus stays on the door. Within seconds, the character comes charging back in for some unfinished business; usually to collect a much-needed object left behind, or to deliver a funny line. Used at least five times per Friends episode.