Finally, I am compiling my own list of etiquette for playing cards with friends. This is not casino or poker-room etiquette, but casual playing-among-friends etiquette.
I am avoiding the topic of betting, because I don't play betting games.
When playing with friends, things can (and should) be much more casual than in casino or more official games. But you must not let the casual atmosphere affect the game to a point where it hinders it/causes confusion, or allows for easier cheating.
I will explain why the rule exist if I feel an explanation is deserved. For the most part, it is to encourage consistency, clarity, and to prevent the possibility of cheating. Be wary of anyone who argues against etiquette If followed, games are clear, everyone knows what's going on, cheating is more difficult, and - while some may seem banal - games will be more efficient, and more fun will be had (frustration diverted).
The focus should of thought should be the game being played. Casual atmosphere allows conversation, but don't let it take over the game (unless everybody is distracted). It is very frustrating for one player to try to play while everyone else is distracted, and even more frustrating for all but one players to be derailed by that one distracted player.
Equipment
Novelty decks. old/crimped/marked/torn/broken/worn-out decks, euchre decks (that is, decks played with games that don't use the whole deck), or decks with non symmetrical backs are frowned upon (Euchre decks are OK for euchre) and should be avoided. Players should be sitting as evenly spaced as they can, unless this is a hindrance such as with long tables. Regardless of table, players should all be about the same space away from the center of play, and unable to peek at each others hands.
Food and drinks should be avoided. Finger food, messy food, sticky food, glasses without coasters, and other items that could mess up the table/cards should especially be avoided. If food is at a table, do not eat during play, but between hands/games, or during dealing.
The Deal
Don't deal slowly, or with an inconsistent pace. A player may just be bad at dealing, but they also may be cheating. With the players I usually play with, it is more likely that they are cheating.
Do not touch your cards until the dealer is done dealing (last card dealt out). The only exception is if the cards are dealt sloppily and you are making clear whose cards are whose.
Dealer should not peek the bottom card, which means (at least on the last shuffle, and all handling after the cut) when the dealer is bridging or squaring up the cards, to do so with the card faces down. Many dealers turn them on the side and peek the bottom card. Not only does this rule prevent an unfair advantage, but even if there is not an actual advantage (Dealer dealing last card to himself) it is still not considered appropriate to let a potentially advantageous maneuver to be demonstrated at a table.
Deal starts to the dealers left and goes in that direction.
Do not begin playing until all players have their cards organized. If you are playing a game (like hearts or P's and A's) that has a certain card played first, that player should still wait for all players to be ready before playing it.
A dealer should ask someone else to cut, and the person cutting should rotate fairly. Dealer asks someone to cut, and they should cut, with only one hand, towards the dealer (into two piles). The dealer should complete the cut (with one hand) and begin dealing. The other person may deny the cut by saying so, in addition to a gesture: a hand wave or tapping the top of the deck.
A
Scarnes cut is not acceptable unless decided on beforehand. It is technically okay but poor to cut only one card.
Playing
Any statements about bidding, passing, calling trump suit, or whatever speaking that actually is part of the game should be loud, clear, and direct. In the game P's and A's, (for example), players may be "drinking" (passing) multiple times. Even so, it should not be assumed that players are drinking, and players skip them and move ahead. The turn order should still pass each player, and each player passes, saying so out loud. Trust me, any time saved by skipping ahead is lost with confusion. Also, players may be passing when they can play, and to skip them may actually be skipping them. And lastly, it's disrespectful.
Be careful of making strange gestures or statements that may be mistaken as some sort of signal. Try not to do this.
Do not bend cards. Do not play cards violently. Do not toss them off-handedly/overly-casually onto the table, and do not bend the cards. Do not play cards in such a way as for them to "fly off" or away. A common move is for players to lean far back and spin the cards to the table from a distance. This is not OK.
When you are still in a a game with a hand, keep the hand above the table. If the number of cards you have is open information (P's and A's, BS, other drop style games), cards should be fanned evenly and not held in a pile. Cards should never be held under the table. If you are out of a game, do not hold your hands clasped in front of you, as others may mistake you for still being in the game. Essentially, do not hold your cards in such a way (intentional or not) that could give you or someone else an advantage.
Do not critique or criticize during the game, unless it is for agreed-on educational purposes. Constructive criticism is to be avoided, unless the other person specifically is trying to learn or asked for criticism. Never give out criticism, critiques (constructive or not) if the other person did not explicitly ask for it beforehand.
It is also improper to praise other players (opponents or partners).
It is improper to give advice to players. This is because it is assuming, pretentious, and condescending. Additionally, you don't want to give advice to a player who may actually be better than you, and playing with a more advanced strategy. Once a player, during P's and A's, kept telling me what to do and how to play (under the impression that I had not played before), and I kept beating him. He congratulated me on my beginners luck for 6 or 7 straight games. Don't be that guy, do not make assumptions on the other players levels of skill.
Do not draw attention to the score, the tricks left to win, or other such information. Ever.
You should not hold a card away from your hand if it is not your turn. That is, even if you know what card you will be playing, do not hold a card separate and out until it is your turn.
Do not go to gather cards until all cards are down on the table. If playing a game where cards are cleared, let the dealer clear them, and always clear them into one pile.
You should not ask to see a hand or trick (ex: folded), unless it is part of the rules of the game.
It is not OK (unless allowed by those playing), for players to ask about previously played cards, previous tricks, or strategically advantageous historical information. This should be avoided, and only really allowed if a player is distracted. Except for historical information, it is OK to ask about open/public information in a game (IE: the number of cards a player has left, current trump, etc). This is OK, (and the information should be given out nicely) but FAR better is to pay attention and take note of this information without having to ask.
Spectating
When spectating, all of the same [applicable] rules from above are still in play. Especially if players are rotating in and out.
The important rules are:
Don't go around the table looking at all of the hands. Don't make remarks about the score, strategy, don't try to give players advice that isn't asked for, don't make guesses or bets on who is winning or what will happen, try not to distract players, don't draw players into side conversations (during more serious games), don't say things like "oh that was a mistake" or "and now he's got the game".
In fact, when spectating, don't talk about the game to anybody playing it. This is more guideline than rule, but I struggle to come up with an example where it is appropriate.
Be respectful.
