Star Battle technique: last candidate
Every row, column and region needs a star.
This is where every solve begins and ends. A row, a column or a region needs exactly one star. As you cross out cells that cannot hold a star, some unit runs down to a single possible cell. That cell must hold the star.
How to spot it
After each star you place, cross out its whole row, column, region and the eight surrounding cells. Then scan every unit for a single remaining cell. Regions are the easiest to overlook because they are irregular, so trace their outline with a finger.
Example
Example from a real Pencilmark puzzle (#4, 5×5). Solver explanation: “Col 3 has only one cell left where a star can go: row 1, column 3.”
Use it constantly; the later techniques exist to create positions where this one applies.