Card counting in Blackjack involves tracking the ratio of high to low cards remaining in the deck to gain an advantage over the house. A common strategy is to assign values to different cards, with high cards (10s, face cards, and Aces) typically assigned a negative value and low cards (2 through 6) assigned a positive value. As cards are dealt, players maintain a running count, which helps them gauge the composition of the remaining deck. When the count is positive, indicating a higher proportion of high cards left, players may increase their bets since this scenario is more favorable for them.