1. Scanning (Cross-Hatching)

Look at the rows and columns within a specific 3x3 box. If a number (e.g., 5) is present in row 1 and row 2, but missing in the box that spans rows 1-3, you know the 5 must go in row 3 of that box.

2. Counting Candidates

Look for a row, column, or box that is almost full. If a row has numbers 1 through 8 filled in, the empty cell must be 9. This is the easiest way to fill in the blanks.

3. Pencil Marking

If a cell could be one of two or three numbers, write them down in small print. This helps you visualize possibilities and spot patterns like "Naked Pairs" later on.