The corner pattern is easier to see and use than other patterns. When you see it you may be able to find twins right off. You can also find single numbers that will help you.
You see a corner pattern when there are four numbers bunched into the corner of a box. The puzzle below shows four corner patterns: the 8625 in box 1, the 2591 in box 3, the 5734 in box 7 and the 2894 in box 9. Boxes 3 and 7 have corner patterns with no additional cells populated, boxes 1 and 9 each have an extra number in them that aren't needed (the 3 in box 1 and the 5 in box 9 aren't part of the corner pattern).
When you find a corner pattern in a box here's how you can benefit from it. Row 9 has five numbers in it, 34586. Notice the 3 and 6 (with green circles). Box 9 doesn't have a 3 or 6 yet. The green circled cells are the only place the 3 and 6 can go so you know those two cells contain 3 and 6.
Now look at the 5182 in column 9. Box 9 already has a 5, 8 and 2. So the only number that isn't yet in box 9 is the 1 (red circled). The 1 therefore can only be in one cell in box 9. That location is circled in red.
Because of what has been found in box 9 so far there is only one cell that isn't filled in or circled. By deduction we know that cell must be a 7.
There are more numbers that can be discovered with the other three corner patterns that haven't been discussed yet. Those are left for you to see if you can find them. Then look at figure 2.
To illustrate how numbers are found look at the puzzle in figure 2 below. The underlined numbers are numbers directly found by using the corner pattern.
This video talks about the corner pattern and shows examples of it.
You can find the corner pattern in puzzles with any skill level but there will be more in easy to hard puzzles than in expert puzzles. Keep in mind though that as you fill in numbers in puzzles of any difficulty it's possible to create corner patterns.
Sudoku - the puzzle that addicts