What are the main poker etiquette rules?

A. Good manners are the oil that makes our lives run smoothly, and they are needed at the poker table as much as - no, more than - anywhere else.
While the great game of poker can be a way of making money, its main purpose is to provide players with a pleasurable experience - to be fun. And it can't be fun if even one of the people you are playing with is rude, offensive, insulting or defiant of either set of rules, of the game and of politeness.
Of course, newcomers might not always know what these rules are, so here is a list, primarily for them. But, even if you are a regular player or hardened pro, please read them: it may be that you may find your own behavior listed as obnoxious. And you might even decide to change it:
Do...
...always be polite: you are among friends and potential friends.
...apologise when you act out of turn or make any other mistake (everyone stumbles at some time or another, just try to keep it to a minimum, and say sorry when you do).
...ask the dealer if you don't know a rule (but try not to give your hand away when you do). Everyone at the table had the same problem when they began playing.
...be alert, watch the game, know when it's your turn. Playing out of turn is a clear signal to your opponents that your mind is somewhere else, not on the game, and they will take advantage of that.
...check out the minimum buy-in; players sitting down without it are the cause of too many disputes.
...deal and discard carefully so that you don't reveal the cards.
...enquire before you smoke, when a table is formed, even when smoking is permitted: there may be a simple reshuffle of seats that puts the smokers together and doesn't upset the non-smokers.
...hide your cards from other players and kibitizers.
...leave your cards on the table: holding them up against you is illegal, as is showing them to kibitzers. Learn to look at them by slightly bending the corner to see what they are, not lifting them right up. And leave your chips on the table, too, even if you are going to away for a while: they won't be stolen.
...listen to your IPod or whatever, if you must, but make sure you can hear everything being said a the table and give the game your absolute priority.
...play as quickly as you can; you're going to have to make up your mind sooner or later, and sooner is better.
...protect your cards as they are dealt to you, by putting your hand or some heavy little lucky charm on them. But don't look a them one at a time as they are dealt - wait until you have received your dull quota of cards.
...remember that silence is always preferable to comment, jokes, chatter, song, or any other diversion.
...."show one, show all": you are required to open your hand to the whole table if you choose to show it to one player; "show one show both" (if turning over one card, turn the other one over, too) is not a rule but doing so avoids your looking like a teasing jerk.
...shuffle fast and short, or shuffle off to Buffalo.
...speak up if an error is being made in decisions or pots. Far from being nosey, it's your duty (but be sure of your facts!).
...tip the dealer, where permitted (in the US it's OK, as it is in British cardrooms but not casinos; it varies elsewhere).
DON'T...
...blame the dealer for your hand - or anything else. He or she is under pressure and under paid. Rude remarks are bad enough, chucking your cards at him or her should get you barred.
...boast or moan during a hand - it can often be helpful to one or more of those still playing (it's better not to do so after the hand, either).
...comment on the hand while it is still in progress. This is actually illegal in most of Europe, if not in the US. Be particularly careful not to point out possible (or actual) straights and flushes on the board..
...give advice or expect it from others. "One player to a hand" is the rule. And don't show your cards during play to a folded neighbor or a kibitzer.
...hide your chips: it is illegal to bet with concealed chips. Keep the higher denominations towards the table, so that everyone can see how much you have left.
...incite a player to call, raise or fold, whether you are in the hand or not; it's the height of bad manners.
...indulge in post-mortems and bad beat stories. Nobody wants to know, even if they pretend to, out of politeness.
....make string bets. All your action has to be in one movement: it's always better to say "Raise" before doing anything with your hands otherwise you risk your raise being disallowed if you do so in two stages.
...mess up the cards: if you eat at the table, use a fork. And if you fiddle with your cards, don't leave one of them bent or even the slightest bit marked. Other players may think you are a professional cheat.
...put chips in your pocket - you must reveal how much you are playing with. And never take them with you when you leave the card-room, it's actually against tournament rules.
...show your hand, except when you are called. Otherwise, during the game it's illegal (being helpful to those still playing). After the hand, it's either boastful or nebbish. It can only reveal your pattern of play, even if you think you are building a misleading image.
...sing, chatter or tell jokes (even good ones) or otherwise make a fool of yourself. You may not realise it but you are suffering from a form of Tourette's Syndrome, where the afflicted are unable to stop themselves from talking out loud.
...slow-roll your hand. Nobody wants be kept in suspense while you turn it up one card at a time: turn it over quickly and neatly.
..."splash the pot" - that's throwing your chips into it, so that other players have to ask whether you have raised, and by how much. You might think it's insouciant, actually it's thoughtless.
...swear. It's always offensive to someone.
...talk on your cellphone when you are supposed to be playing. Nobody wants to hear your conversation. Everybody wants you to pay attention to the game.
...tell a loser how they should have played. Not only is it arrogant, it is silly to educate someone who might make the mistake again, to your profit.
...touch another player's cards or chips except when he is absent from the table and must ante or fold.
...try to change your call after you have made it. If you say "raise" you've got to raise, even if you didn't realise there was already a raise - it's your responsibility to pay attention.
...turn over undealt cards in the deck after a hand, to see what you would have had (or ask the dealer to do so). It holds up the game and is invariably disappointing.
AND, ONLINE...
Don't ask for email addresses or offer yours. That can get you barred.
Don't complain about slow players. The delay could well be in a poor connection.
Don't collude, like raising a friend (or yourself on another computer) to a dizzy amount in order to force out a third player; website detectives are watching.
Don't create extra accounts. It can get all your accounts frozen.