Never quit.
If you're about to die, do anything you can to hurt the one who killed you. Attack him, support his enemies, attack his friends, sacrifice your pieces to his enemies. When you're losing your mantra should be "... to the last, I grapple with thee; from hell's heart, I stab at thee; for hate's sake, I spit my last breath at thee...". Do whatever you can to hurt him, but don't ever quit the game.
Trust no one.
Be paranoid - always look for the stab.
Always look for a stabbing opportunity.
Watch your back.
Paranoia is a fickle friend.
Never stab half-heartedly. A double backstab with +2/+2 poisoned blades is far more effective than a single stab with a penknife (Speaker used to have (be?) a 4/4 thief/assassin - the DM wouldn't let the assassin out to play very often though).
Use the big map, there's more on it (click the square beneath the normal map). Use the orders history (links are at the bottom of the game page).
Never accuse a player of cheating on the forums. Email the mods instead (
[email protected]).
Oh, and never ever quit a game. Ever.
Enjoy it. It's only a game.