Some of these are from Roger Ebert, some are my own.
The Bar Fight Rule
When a fight in a bar breaks out, nearly everyone in the place begins fighting, spontaneously and without cause -- even with people they’ve have been sitting next to for some time.
The “Heroes With Clippings” Rule
Movie heroes always keep a file of newspaper clippings that detail their downfall. They like to pull out this file and go through the clippings again from time to time, just to refresh their memory. Often they will pay special attention to one clipping, at which time we will be shown a flashback to the event in the article.
The Alarm Clock Rule
If an electric clock is given a close up, it will be either twenty-nine minutes past the hour, or one minute to the hour. The time will progress one minute, waking up the hero with a song that is important to the plot. (Groundhog Day, Back To The Future)
The Lurch Awake Rule
If you are a movie character and you have a bad dream, you can’t just wake up by opening your eyes. No, you must sit up quickly, sweaty, eyes bulging, mouth agape.
The Girl Back Home Rule
In a war movie, the guy who shows the hero a picture of his girl back home and says, “I’m gonna marry her when all this is over” – that’s the guy who’s as good as dead in the next scene. It’s the war movie equivalent of red shirts in Star Trek. (Platoon, We Were Soldiers). Ditto the guy who carries a letter to his family and asks his buddy to mail it for him in case he dies. Goner. (Saving Private Ryan, The Thin Red Line)
The Baguette Rule
Any time a movie character is shown walking home with a bag of groceries, the bag is paper and contains a tall, fresh baguette –- which flies in the air when the character has to jump out of the way of a car driving down the sidewalk.
The “We've Been Expecting You” Rule
Whenever a hero fights his way into the villains fortress, escaping multiple assassination attempts, he will be caught and taken to the villain, who will invariably greet him with, "We’ve been expecting you." (most Bond movies)
The “It’s Quiet” Rule
Anytime characters are in a perilous situation and one says, “It’s quiet,” someone else will invariably reply, “Too quiet.”
The Rainy Epiphany Rule
The best way for a movie character to demonstrate that he has had an epiphany or dramatic change of heart is to stand outside in a heavy rain shower and lift his face and arms to the sky. (The Shawshank Redemption was the first, I think, but it has been copied many times by others like Cuba Gooding in Instinct).
The "Tell Me Where You Are And I'll Come And Get You" Rule
Telltale line that finally makes obvious to everyone (except the hero) that the hero’s trusted friend or supervisor has gone over to the bad guys. (F/X)
The Media Coverage Rule
All media coverage depicted in a movie will prominently feature the main character, no matter how incidental his or her involvement is to the big story. His picture makes Page One, and CNN thoroughly documents his simple presence in a crowd. (Godzilla -- TV news reports pass up footage of a giant rampaging lizard in favor of shots of Matthew Broderick carrying his luggage, digging a hole, etc.)
The Angelic Priorites Rule
Modern movie angels mostly seem to visit earth in order to smoke cigarettes, eat pizza, and show what regular Joes they are. Although famine, war and disease torment the globe, these angels visit to solve more pressing problems, like a guy who has stopped dating because he’s lost his faith in women or a sports team that needs to win the big game. (Michael, It’s A Wonderful Life, Angels In The Outfield)
The Movie Lot Rule
Any scene that takes place at a movie studio lot will feature costumed extras milling about, including at least two of the following: a knight, a cowboy, a man dressed as an Arab, a Marilyn Monroe lookalike, an alien, Roman soldiers, Abraham Lincoln, Napoleon, or women in a scanty slave-girls costumes. (spoofed in Pee Wee's Big Adventure)
The Big Names Rule
When an entire trailer or poster for a movie consists of the names of the two stars, as in STALLONE-STONE or WESLEY-WOODY, this suggests that getting those two names represents most of the films budget, and that funding a good script was a lower priority. (The Specialist, White Men Can’t Jump)
The Bilingual Nazi Rule
Nazi officers always speak English when talking to each other, even though Nazi sergeants can be heard in the background barking orders in German. (any classic WWII film)
The Late Pregnancy Rule
Any character more than seven months pregnant will give birth by the end of the film, usually in an unusual place, such as an elevator, a cemetery or the back seat of a taxi in a traffic jam. The baby is always delivered by someone squeamish and inexperienced.
The Wet Dog Rule
All wet dogs shake themselves dry only while standing next to well-dressed movie characters. If the dog is huge and especially dirty/muddy, the shake will be shown in slo-mo. (Beethoven)
The Shattered Vase Rule
Anyone holding a vase, glass, coffee mug or other breakable object will drop that object upon hearing bad news. Usually the object will fall and shatter in slow motion, typically from multiple angles.
The Discarded Newspaper Rule
If you time-travel in a movie and aren’t sure what year it is where you land, just look for a trash can, where you can always find a discarded newspaper with the date. (Back To The Future)
The Chinatown Rule
In any Asian city, or any city with a Chinatown, all chase scenes happen to occur on Chinese New Year, and lead directly through a parade.
The Hospital Rule
If a hit man has to kill someone in a guarded hospital room, all he has to do is into a linen closet, emerge wearing a lab coat and carrying a clip board (both freely available in any hospital linen closet), and walk around the hospital as if invisible.
The Psychotic Collage Rule
Psychotic stalkers sublimate their destructive impulses by creating a collage of newspaper clippings, candid photos and charcoal sketches of their victims, and maniacal scribblings or poems scrawled on paper. This collage is glued to the wall of the psycho’s one-room apartment, to be found by police officers bursting in just after the stalker has fled, letting them know exactly what the killer is up to. (Se7en, In The Line Of Fire)
The Karma Rule
The more detestable a movie villain is, the more gruesome his ultimate death will be. (Terminator crushed in The Terminator, Billy Zane shot in the mouth with a flare gun in Dead Calm, Ronny Cox’s head bulges and explodes in Total Recall, Tony Goldwyn impaled by falling broken window pane in Ghost)
Got any others?