SLEEPYHEAD RULE

The teenaged male lead will begin the first day of the game by oversleeping, being woken up by his mother, and being reminded that he's slept in so late he missed meeting his girlfriend.
"No! My beloved peasant village!"
The hero's home town, city, slum, or planet will usually be annihilated in a spectacular fashion before the end of the game, and often before the end of the opening scene.
Thinking With The Wrong Head (Hiro Rule)
No matter what she's accused of doing or how mysterious her origins are, the hero will always be ready to fight to the death for any girl he met three seconds ago.

CUBIC ZIRCONIUM COLLARY

The aforementioned mysterious girl will be wearing a pendant that will ultimately prove to be the key to either saving the world or destroying it.

SINGLE PARENT RULE

RPG characters with two living parents are almost unheard of. As a general rule, male characters will only have a mother, and female characters will only have a father. The missing parent either vanished mysteriously and traumatically several years ago or is never referred to at all. Frequently the main character's surviving parent will also meet an awkward end just after the story begins, thus freeing him of inconvenient filial obligations.

SOME CALL ME...TIM?

Good guys will only have first names, and bad guys will only have last names. Any bad guy who only has a first name will become a good guy at some point in the game. Good guys' last names may be mentioned in the manual but they will never be referred to in the story.

LUDITE RULE (OR, GEORGE LUCAS RULE)

Speaking of which, technology is inherently evil and is the exclusive province of the Bad Guys. They're the ones with the robots, factories, cyberpunk megalopolises and floating battle stations, while the Good Guys live in small villages in peaceful harmony with nature. (Although somehow your guns and/or heavily armed airships are exempted from this.)

LET'S START FROM THE VERY BEGINNING RULE (YUNA RULE)

Whenever there is a sequel to an RPG that features the same main character as the previous game, that character will always start with beginner skills. Everything that they learned in the previous game will be gone, as will all their ultra-powerful weapons and equipment.

THE HIGHER THE HAIR, THE CLOSER TO GOD (CLOUD RULE)

The more outrageous his hairstyle, the more important a male character is to the story.

GARRETT'S PRINCIPLE

Let's not mince words: you're a thief. You can walk into just about anybody's house like the door wasn't even locked. You just barge right in and start looking for stuff. Anything you can find that's not nailed down is yours to keep. You will often walk into perfect strangers' houses, lift their precious artifacts, and then chat with them like you were old neighbors as you head back out with their family heirlooms under your arm. Unfortunately, this never works in stores.

HEY, I KNOW YOU!

You will accumulate at least three of these obligatory party members:
The spunky princess who is rebelling against her royal parent and is in love with the hero.
The demure, soft-spoken female mage and healing magic specialist who is not only in love with the hero, but is also the last survivor of an ancient race.
The tough-as-nails female warrior who is not in love with the hero (note that this is the only female character in the game who is not in love with the hero and will therefore be indicated as such by having a spectacular scar, a missing eye, cyborg limbs or some other physical deformity -- see The Good, The Bad, And The Ugly Rule.)
The achingly beautiful gothy swordsman who is riven by inner tragedy.
The big, tough, angry guy who, deep down, is a total softy.
The hero's best friend, who is actually much cooler than the hero.
The grim, selfish mercenary who over the course of the game learns what it means to really care about other people.
The character who is actually a spy for the bad g