Optimal play in blackjack, particularly when considering the dealer's upcard, relies on several key principles. Players should assess the strength of the dealer's upcard, as it influences both the likelihood of the dealer busting and the strategies available to the player. Generally, weaker dealer upcards (like 2 through 6) suggest a higher chance of busting, prompting players to adopt a more conservative strategy, while stronger upcards (7 through Ace) may necessitate a more aggressive approach.