Things learned from experience (not always my own direct experiences, though):
Don't spill beer on your game books
If playing by candle light, don't spill the wax from the enormous candle you got at Wicks and Sticks in the middle of the table
Don't stick your nasty, smelly unshod feet under the GM's chair in the middle of summer without air conditioning
Don't dump cactus needles down your neighbor's plumber's crack - you'll only get strangled for it
Don't laugh too loudly in the late hours of the night at a player's house because you will only be thrown out by a cranky man in tan boxers