To bet more when the deck is favorable in blackjack, you first track the running count by assigning values to the cards as they are dealt. Then, you calculate the true count by dividing the running count by the number of decks left in the shoe. A higher true count indicates a favorable deck with more high cards, which gives you a better chance of winning, so you increase your bet accordingly. The key is to gradually adjust your bet based on the true count, managing your bankroll carefully and avoiding large jumps in bet size to prevent drawing attention.