Double down is to double your bet and receive only one more card. This move is recommended to use when you have a hand with a total count of 11. This way, you have the chance to hit 21 or come close to it. You can also use this move when you have a soft 16,17 or 18, and the dealer shows a lower card. When not to make this move, the dealer is showing an ace because the chances of the dealer getting a blackjack are high or get a number count more than yours.