Deciding the Order
Tag teams should sit next to each other with their opponents opposite. A coin toss decides which team goes first, but it is up to each tag team which player goes first. Once this is decided, player 1 from team A has a turn, then player 1 from team B. Next it is player 2 from team A and then finally player 2 from team B has a go. The fourth player to move is the first player allowed to conduct a battle phase.
Attacking and Defending
You can attack an opponent of your choice when it is your attack. It doesn't matter if one opponent has no monsters to fight; you can attack the opponent directly in this situation. It is also possible to protect your teammate from direct attacks. This is called a team defense and must be declared straight after an attack has been used. You can only defend in this way of you have monsters but your teammate does not. Your opponent can no longer attack your teammate, but is free to attack your monsters.
Reading the Cards
Since the cards are made for single duels, you will have to read them differently to play a double duel. Each player now has a quarter of the dueling field rather than half, so anything that mentions your side of the field must be taken as your quarter. If it talks about your opponent's side, then choose one of your opponents' quarters. Choose an opponent for cards that mention your opponent. Sometimes cards will use the term "both players;" select one player from both teams in times like these.
Using Spells
It's possible to use spell cards during your teammate's turn, but it must be in either the first or second phase. Your teammate has the final say on whether this will happen, but you are free to advise. Using your spell card in your teammate's turn will use up the turn, meaning once you are finished it will be an opponent's go.
Elimination
Players are eliminated from the game when they lose all of their life points or can no longer draw cards from their deck. The teammate would fill in for any eliminated player's turn, meaning the order would remain team A, team B, team A, team B. Once both players on a team are eliminated, the other team becomes the winner.