Techniques 2: Very basic techniques and simple questions

1. First look at the rows, columns, and boxes with the most filled-in squares. The logic is easier with fewer options.
2. When you fill in a square, check the column, row and box. Make sure all the other 8 values will not work in that square. It is easier to avoid mistakes than re-solve the puzzle when you find a contradiction.
3. Pencil in which numbers are open for each row and column. If a column and row share one number at a blank, there you go!
4. When cross-checking the rows and columns (tip #3), rule out the numbers that are already in the box.

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