Whenever a card's text directly contradicts these rules, the card takes precedence. The card overrides only the rule that applies to that specific situation. The only exception is that a player can concede the game at any time (see rule 104.3a).
When a rule or effect allows or directs something to happen, and another effect states that it can't happen, the "can't" effect takes precedence.
Example: If one effect reads "You may play an additional land this turn" and another reads "You can't play lands this turn," the effect that precludes you from playing lands wins.
Adding abilities to objects and removing abilities from objects don't fall under this rule. (See rule 113.10.)
Any part of an instruction that's impossible to perform is ignored. (In many cases the card will specify consequences for this; if it doesn't, there's no effect.)
If multiple players would make choices and/or take actions at the same time, the active player (the player whose turn it is) makes any choices required, then the next player in turn order (usually the player seated to the active player's left) makes any choices required, followed by the remaining nonactive players in turn order. Then the actions happen simultaneously. This rule is often referred to as the "Active Player, Nonactive Player (APNAP) order" rule.
Example: A card reads "Each player sacrifices a creature." First, the active player chooses a creature they control. Then each of the nonactive players, in turn order, chooses a creature they control. Then all creatures chosen this way are sacrificed simultaneously.
If an effect has each player choose a card in a hidden zone, such as their hand or library, those cards may remain face down as they're chosen. However, each player must clearly indicate which face-down card they are choosing.
A player knows the choices made by the previous players when making their choice, except as specified in 101.4a.
If a player would make more than one choice at the same time, the player makes the choices in the order specified. If no order is specified, the player chooses the order.
If a choice made by a nonactive player causes the active player, or a different nonactive player earlier in the turn order, to have to make a choice, APNAP order is restarted for all outstanding choices.