Learn / Sudoku
Find naked singles
A naked single is an empty cell with exactly one remaining candidate. Check the cell's row, column, and box. If eight different digits are excluded, the ninth is the answer. Place it and update connected notes. A cell with two candidates is not a naked single, even if one candidate looks more likely.
A checked example
Row 1, column 7 takes 3. Every other digit is already excluded by its row, column, or box.