These Sudoku solutions techniques are for the serious Sudoku addict!
These are very involved tactics and require extensive knowledge of Sudoku puzzle strategy.,
they are slightly different from strategies such as elimination, CRME, lone rangers, etc, in that they
do not follow the standard subgrid, row, column recognition patterns involved with the afore
mentioned solution types.
XWing
To solve Sudoku puzzles using this process, one must have recognition of number relationships
in the grid. To begin with the name X wing refers to the top right corner and bottom left corner, or the bottom
left corner and top right corner, which form an X, hence xwing.
THEORY:
The theory goes something like this:
(For one, we know that for any unique sudoku solution, the numbers 19 can only appear once in any
given row, column, or subgrid.) So for sudoku solutions with this method proceed as follows:
If the number, say y, appears only twice in any given row, then we know it CAN only appear in
one of those two rows.
Further if y is also restricted to two columns (and no more than two columns) , and since y can
only appear once within each of the two rows, no column can have more than one y, and y will
appear only once in each of the columns contained within the rows, and any other candidates
in those columns can be eliminated.
(The converse of this theory also holds, that is interchange the words row and column above).
Perhaps an example will suffice. Consider the following Sudoku puzzle:
XWING THEORY :

In this example we have highlighted all the possible values for our candidate (the number 6). Looking at the diagram we can observe the following:

Swordfish
Similar to an xwing pattern, the swordfish theory proceeds as follows:.
Given a general puzzle with three rows that has candidate y, in each of the three rows: then y must be
restricted to the same three columns within those rows and:
three rows. (Therefore any other y's within those columns can be eliminated.)
Finally, as it was true for the xwing, the converse is also true ( that is interchange the words, rows and columns) ,
and the theory holds. Again, here is the graphic example:
SWORDFISH:

In this example we have highlighted all the possible values for our candidate (the number 5). Looking at the diagram we can observe the following:

XYWing
Extends the xwing theory to include three cells as follows:
Given three cells:
with the other two candidates yz, xz).
Then any other cell which shares a group with both branch cells can exclude the z element that is common
to both branch cells.
Proof: If a root cell sharing a group with both branch cells has member 'z', then neither branch can be
assigned 'z'. Consequently one branch is assigned x and the other y, leaving the root without a
valid member.
Note: If all 3 cells in an xy wing share the same candidates (namely x,y,z), then this would reduce to a
simple triplet or naked triple.
Of course it may be easier to visualize, refer to the diagram below:
XYWING THEORY:

In the diagram we have labeled cell A (root cell) containing {2,5 ,8}. Also we have the two branch cells as B which contains subset {2, 5} and C which contains subset {5,8}. Therefore by the xy theory, we can safely eliminate 5 from those cells within the group contained by A,B, and C. ( This cell is highlighted in red ). 
Colors Technique
An interesting little technique, basically used to try to narrow candidates only in two cells within a given
group ( say subgrid, row, or column). the two cells would have a conjugate, or opposing relationship, that is,
when one is true , the other is false. The idea of the colors technique in essence then is to assign colors to
these variables , or states.
For any given sudoku there may be any number of these 'conjugate pairs' present at any given time.
Some may even link together forming a chain of alternate truefalse cell states, and these chains may expose
candidates which can then be excluded safely.
Note: Whenever two cells within a group ( subgrid, row or column), have the same color, this would indicate
the color must be the 'false' color, since this is impossible, or an illegal state.
Again we provide a visual example to clarify the discussion.I
COLORS TECHNIQUE

In this diagram we choose to start with row2 column2, and assign it color green , it's conjugates at row2 column3 and row6 column2 are then colored blue. We proceed around the grid in a like manner. With this method we see that the blue color has more than one member in a subgrid, therefore the blue nine's must be false and we can now safely add the green colored nines. 
BRUTE FORCE ALGORITHMS:
There are approximately 67,000, 000, 000, 000, 000, 000, 000( YES, that is 6.7 x 10 to the 21st power)
Sudoku puzzle solutions (or game combinations) possible.
BruteForce algorithms are basically computer programs that will solve Sudoku puzzles.
A good program might be a practical way to solve Sudoku puzzles, (so long as the puzzle is a valid one,
that is one of the 6.7 x 10^ 21 grids).
Basically it is a numbers crunching game,
A brute force algorithm visits the empty cells in some order, filling in digits sequentially from the
available choices, or backtracking (removing failed choices) when stymied. For our purposes
assume a algorithm order of left to right, top to bottom. (The algorithm could, however,
visit the empty cells in any order)
Briefly, a brute force program(or a person doing it manually) would solve a puzzle by placing the
digit "1" in the first cell and checking if it is allowed to be there. If there are no violations
(checking row, column, and box constraints) then the algorithm advances to the next cell, and places
a "1" in that cell. When checking for violations, it is discovered that the "1" is not allowed, so the value is
advanced to a "2". If a cell is discovered where none of the 9 digits is allowed, then the algorithm leaves
that cell blank and moves back to the previous cell. The value in that cell is then incremented by one.
The algorithm is repeated until the allowed value in the 81st cell is discovered. The construction of 81
numbers is parsed to form the 9 x 9 solution matrix.
Most Sudoku puzzles will be solved in just a few seconds with this method, but there are exceptions.
SUMMARY ADVANCED SUDOKU SOLUTION TECHNIQUES:
These are the main Advanced Sudoku Solution techniques.
Although we have only mentioned the four main ones, there are many many more ;
however we do not believe these techniques are effective as the basic techniques,
including simple Elimination, CRME, Twins, Triplets and Brute force.
All of those techniques should give you enough muscle to solve a majority of Sudoku puzzles
with ease. To review those techniques simply click here.