Go through the left card picture by picture: is this picture on the right card too?
That way you find the match for sure, even when it is small or turned.
Once you find it, circle it on both cards.
Looking back and forth at random takes longer and you easily miss something.
Example
For parents
What does this exercise practice?
The common picture practices systematic comparison: working through in order instead of jumping around.
Common pitfalls
The same picture can be a different size and turned a different way on each card. Similar pictures are easily confused; before circling, check once more.
How to practice at home
Make two cards with eight drawn pictures each that share exactly one picture - and let someone else search.