Much like the RPG Cliche list, these are a set of non-rule rules to help anyone who is new at a tabletop RPG.
Rule Prime - All The World Is Your Enemy: The GM is cruel, incompetent, trying to railroad you through a pre-planned path, or any combination of the three. The other players are useless noobs or cutthroat munchkins out to kill their fellow PCs (and steal their stuff!), and you'll have to be an even better one to survive. Coherent plot and story, let alone any kind of collaboration between GMs and Players is a pipe dream. Trying to talk to the group about any concerns can only make them worse. The guy who brought snacks is actually a government assassin wearing a rubber mask, and the snacks are deadly poison. This is the underlying assumption behind the rest of this list - if it doesn't apply to your gaming group, not only might this list misinform you, it might send you into a spiral of suicidal depression from which your love of gaming never recovers. On the other hand, if you live in a webcomic of any kind, this is always true.
Rule 0 - Don't Give The GM Ideas: Keep your mouth shut. This seems mean to the player, until you run into a situation like this:
GM: You encounter a hooded figure.
Group: Aww... no!
Bill: It's alright guys, as long as it's not the Darkshroud of Darky Darkness, we'll be fine.
GM: (Devilish smile)
Group: (Collective gulp)More players have been killed by giving ideas to the GM than have been killed by pre-planned traps, encounters, and bad rolls.
Rule 00 - The GM is Always Right: No matter how eloquently the Rules Lawyer states his case for the loophole he's trying to abuse, the GM always has the last word.
Rule 000 - ...But No Players Means No Game: Having the last word doesn't mean the GM can lord it over the players like a tin-pot dictator. Like any other governing body, abuse of power will eventually lead to a coup d'état.
Rule 1 - Don't Assume: Never assume that the Mook is alone/just a mook. Never assume that the treasure room is trap free. Never assume that the GMPC you're traveling with is actually on your team. Because...
Rule 2 - Everything's a Trap: The Mook is a decoy. The Treasure Room is actually the mouth of a monster. The GMPC is part of an underground conspiracy to kill you. The ship you're on is a secret pirate ship. The ruins are rigged to fall at any second. The gem will steal your soul. The treasure chest has a trap in it. The trap you bought for your Ranger to use is actually rigged to trap you.
Rule 3 - Know Your God: If your GM has just started playing Star Wars: Knights of the Old Republic, start playing it too. It's likely that some element from it will come up in some way or another.
Rule 4 - Cautious Bell Curve: Works something like this:
Rule 5 - Rules of Gracious Gratuity: Never trust a GM who lets you hand-pick your starting equipment. It means one of three things:
Rule 6 - Bought Offerings: Game Masters are the Gods of their worlds. As such, they can be given an offering to help them rule in your favor.
Rule 7 - Inverse Characterization Rule: The more backstory you've created for your character at the beginning of a campaign, the less likely it is to come up during actual game play, and may require you to start a monologue to let the other players know just how awesome your character's life was.
Rule 8 - Book-Worm's Victory: Most people are too lazy to look up the actual spell. So always trust the one guy in your group who has actually read the spell book cover to cover.
Rule 9 - Door to Nowhere: All doors lead to exactly where the GM wants.
Rule 10 - Dead Kid Rule: No NPC is ever safe from dying. If the GM wants to kill them to shock you, he will.
Rule 11 - Don't Break God: Never put your GM in a position that he hasn't planned for. His improvisations usually prove to be deadly.
Rule 12 - Let Kindness Happen: If your GM is a kind GM and he gives you lots of things, be gracious and never point this out. Nice GMs tend to be very clumsy when they ratchet up the threat level. Things break.
Rule 13 - Dice Sounds are Bad: If you hear dice rolling behind the GM screen, be very wary. Something is about to ambush you.