This is a good one.
When practicing you sometimes come to a difficult section which slows you down or stops you. Instead of starting from the beginning of the piece again, take the difficult section and play it slowly 3 times without making a mistake. Should you make a mistake during any of the 3 times then start the 3 times again. Continue until you can play it the 3 times without making a mistake. The next day try again, and if you complete the 3 times successfully then increase the pace until you can play the section at the same speed as the rest of the piece.
The ‘game of threes’ is an excellent way to improve your concentration and accuracy. Remember that good pianists always go straight to the tricky parts of a piece and practice those first.
If you are going to perform the piece eventually then try playing the game of threes for the whole piece.