Shuffle cards. Players sit in a circle. Deal each player one card face up. Player with lowest card starts as dealer. Aces low, CDHS order (Clubs lowest, followed by Diamonds, Hearts, Spades). Shuffle the cards again.
The next player, clockwise from the dealer, guesses what the card on top of the deck is. If the player is correct, the dealer drinks. If the player is wrong, the dealer tells the player whether the card is higher or lower than the player's guess.
The player guesses again. If their guess is correct, then the dealer drinks half a drink and the card is shown face up/discarded. If their guess is wrong, the dealer shows the card face up and discards the card. The player drinks the difference between the number they guessed and the actual value of the card (e.g. Card shown is a 3, player's guess is 7. Player then drinks 4 drinks).
The game then rotates to the next player, clockwise and Steps 2+3 are repeated. If 3 players in a row fail to correctly guess the card, then the player to the left of the dealer becomes the dealer. Game is played until the deck is exhausted.