There are actually only 7 techniques that combined will solve any puzzle....

For an in-depth video tutorial teaching you the most advanced Sudoku Secrets Take a look at the Sudoku Video.

Exclusion [Singleton]

1	2	3	4	5	6	?	8	9

Simply put, if there is only one option for a cell, it must be that option.
Likewise, that option is not allowed for other cells in a given constraint(row, column,grid)
In this case, the cell in question (?) can not be a 1,2,3,4,5,6,8 or 9 so it must be a 7.

This alone will solve the easy puzzles.

Uniqueness [Singleton]

1
			1
	8							?
			6			1
				?
			2				1
					42

The reverse of exclusion, here the cell in question could be any number, but it is the only cell in the grid that could be a 1, therefore it must be the 1 for that grid.


These two techniques will solve most medium & hard puzzles

1	2	3				?	-
*	*	6	-	-	-	-	-	-
7	8	9		4			-
							-
							-	4
							-
						1	*	7
						2	*	8
						3	6	9

Exclusion [Doubles]
two options for two spaces affecting others
Here is a variation of the above but for doubles. Namely, you have two spaces with only two options [4 & 5] therefore the rest of the constraint (column, row, grid) must have neither the 4 or the 5.

Exclusion removes options from the other cells (-) in a constraint.

	?	*
		*		3
		6						3
2
9
	2
	9
3

Uniqueness [Doubles]
two options for two spaces affecting self
Again, an other variation of the above uniqueness, here we have two spaces (*) which are the only spaces in which a 2 or a 9 are possible for the constraint (grid) therefore, the remaining numbers 1,3,4,5,6,7,8 must be removed, leaving the ? cell the only one where a 3 is possible.

Uniqueness removes options from the unique cells in question.

1	2	3				?	-
			-	-	-	-	-	-
7	8	9		4			-
							-
							-	4
							-
						1		7
						2		8
						3		9

Exclusion [Triples]
three options for three spaces affecting others
Variation of the above but for triples. Namely, you have three spaces with only three options [4,5 & 6] therefore the rest of the constraint (column, row, grid) must have neither the 4,5 or the 6.

Be aware that this can show up in a slightly trickier form of three cells, three options such as
[4,5] [4,6] [5,6]. This is harder to recognize than the more repetitious [4,5,6] [4,5,6] [4,5,6]

Exclusion removes options from the other cells (-) in a constraint.

	?	*
		*		3
		*						3
2
9
6
	2
	9
3	6

Uniqueness [Triples]
three options for three spaces affecting self
Again, an other variation of the above uniqueness, here we have three spaces (*) which are the only spaces in which a 2,6 or a 9 are possible for the constraint (grid) therefore, the remaining numbers 1,3,4,5,7,8 must be removed, leaving the ? cell the only one where a 3 is possible.

Again, remember that three options for three spaces could also be [2,9] [6,9] [2,6,9].

Uniqueness removes options from the unique cells in question.

*	^	^
*	^	^
*	^	^
1
2
				8
4
5
							8

Cross Constraints
Row or Column intersecting a Grid
This is an interesting issue where a grid is intersected by either a row or a column. In this case, the 8 must appear with in the intersection (*'s) of the cross constraints, and therefore must not occur in the non-shared cells of the two constraints (^)

With these 7 techniques you can now solve ANY sudoku puzzle