Fill the grid so each row contains the digits 1 through 9 exactly once
Fill the grid so each column contains the digits 1 through 9 exactly once
Fill each 3×3 box so it contains the digits 1 through 9 exactly once
Use the given numbers as fixed clues
Place only one number in each empty cell
Eliminate numbers that already appear in the same row, column, or box
Look for cells with only one possible number
Scan rows, columns, and boxes for missing numbers
Repeat the process until the puzzle is complete
Do not guess unless you are certain or using advanced solving methods