One of the things I that drove me crazy about Sudoku is how difficult it is to return to a puzzle if you get interupted. This system allows you to walk away from a puzzle at any time and return exactly where you left off.
Step 1: What you need to begin
1. A sudoku puzzle. I enlarged this one (which was the puzzle that appeared on Sudoku.com on July 8, 2006.) to make photography easier. I find this system works better on larger puzzles.
2. A pencil, Not a pen. A pencil.
3. An eraser.
Step 2: Fill in the "Missing Grid"
Enter the numbers 1 through 9 in a "tic-tac-toe" pattern in every blank box.
Step 3: Erase "Across"
So the first number (in the upper right corner) is a "6". Erase every other "6" in that row. Once you have completed the erasing, draw a line across the top of the number to indicate that you have cleared out that line.
Step 4: Erase Down
Step 5: Erase "All Around"
Now you have eliminated all the sixes from all the other blocks. That indicates that a Six canot appear in any of those blocks.
Keep going, repeat those same three steps for all the other pre-printed numbers in the puzzle.