Always create a 21 when you have the chance to Keep as many open columns as possible to reduce your chance of having to discard. Remember that 16 of the 52 cards have a value of 10 so try to create columns with 11 in them, which will combine with any 10 to form a 21.
There are only 4 aces; try to keep track of how many you've seen so far.
Similarly, try to remember how many of the two Black Jacks are still left.
