There are 56 halves in the Double-6 set. Each number appears 8 times.

The number 6 is shown 4 times in the figure. Since there are 8 six's in all, there are 4 more six's to play. The dominoes with six dots on one half that are not yet played are the 6-5, 6-4, 6-3, and 6-2.

The number 5 is shown twice. It would be logical to try the dominoes with a 5 next.