Practice with worksheets. Once you have mastered the flash cards, try your hand at some worksheets. Start by practicing with one number set at a time. When you have mastered all of them, try worksheets that mix up all of the number sets and see how you do. If you know your tests will be timed in school, try practicing with a timer.
If you make your own, you can just draw three circles on a page and then 2-5 triangles on a page, and ask the child to match each circle with a triangle by drawing a line from shape to shape. Vary the shapes and the amounts. Sometimes the amounts should be equal, sometimes not.