The written rules of Spades cover 90% of a game. The unwritten rules cover the other 10%, and violating them is how you get uninvited from next week's game. Nothing is more universal than 'don't trump your partner.'
Don't trump your partner
If your partner is already winning the book with a high card, do not cut in with a spade. Ever. You're not taking a new book — your partner already had it. You're just burning a trump you'll need later.
This is the number one etiquette violation in Spades. Do it once and you'll get told. Do it twice and your partner will bid differently around you for the rest of the night.
Don't table talk
No 'I wish I had another spade' before you play. No 'take that book' when you follow suit. No commentary on what's in your hand. The information has to come from cards, not words.
Trash talk is different — trash talk is about the game state, not the cards. 'Y'all are cooked' is fine. 'I have three spades left' is a violation.
Don't drag your feet
Bid promptly. Play promptly. Don't stare at your cards for two minutes on a routine book. If you need time on a big decision, take it — but respect that everyone else at the table wants to play more than one hand tonight.
Don't renege on purpose
Reneges happen by accident sometimes. Reneging deliberately — hoping nobody notices — will end your reputation at any serious table. If you get caught (and you will), the penalty is a set and the trust never comes back.
