There are methods and certain algorithms that can be used to complete the sudoku puzzles. Many people use different strategies each time they do a sudoku puzzle. Some of these methods include the place finding method, the method of preemptive sets and the candidate checking method.
However, these methods are easy to apply to solving the sudokus, but they do not work every single time. The best algorithm to use where it will work is to place numbers already in all of the squares. Then start working with these numbers by erasing and writing other numbers in them so that they apply to the rules. Not all methods work and some methods that do work every time are difficult and time consuming to do.