Techniques overview
There are dozens of different techniques you can use to help you solve a Sudoku puzzle. Some are great, some are useless, and some just have some pretty interesting names. I have studied most of them, and put together a "short list" of all the ones you really need. In the next two sections ("Basic Techniques" and "More Advanced Techniques"), I will illustrate and explain each one.
Truth be told, "Basic Techniques" alone will give you enough knowledge to solve most of the puzzles printed in all the world's newspapers and magazines.
The "More Advanced" section is there for people who really love cool logic. They will of course help you solve even harder puzzles, but knowing that section is by no means necessary to be great at Sudoku!
In general, techniques can help you do one of two things: they can immediately solve a cell, or, more often, they rule out possibilities, or candidates, for a cell.
Obviously, solving a cell is preferred, but once all the visually recognizable "blanks" are filled in, you will need to move on to candidate elimination if your puzzle still has unsolved cells.
Here is an example of candidate elimination: Let's say you have an empty cell that you know is either a 2, 4, or 9. You will use certain techniques to eventually rule out two of those candidates — usually one at a time. The cell is solved indirectly.
It can be slow work at times, but believe me: What really makes Sudoku so fun and addictive is the process of solving the puzzle, not filling in that last empty cell.
OK, enough talk. Let's get on with the techniques themselves. Please click "Next" to move on to "Basic Techniques."
