I use the Major System, so i will explain this technique.
I have a image or element for every number (1-99)
My Images words are in Spanish but over here are in English.
You can get images of the Major System, is a excellent idea
The game have a variable n-back: the number of current variable n-back is over the image, and below is the current image number (first image, second, ...)
I link the image in the example two people in black with my first element of the Major System 1=Tie. Then I see Two People joined by a tie and they can´t disjoin.
And click on next.
Then I link the image 2 for example oil barrel with the second element in my Major System Noah, for example a oil spilled in the Noah's ark (The animals fall)
If the image 3 have a variable n-back=2 I do a calculation (3-2=1) Then I remember the first Major System element Tie and if the history (tie-two people in black) repeats (in the component of current image) I click on Image match (or press key L) . If not I click on next. And So on.