A safe line does not create a third side
A box with three sides offers a point and another move when closed. The player drawing the third side usually gives this opportunity away. During the opening, choose lines that do not bring either affected box to three sides.
An internal line belongs to two boxes, so inspect both. A boundary line touches only one, although it still shapes later chains.
A third side can give away several points
The same player moves again after scoring. If closing one box exposes the fourth side of its neighbor, several points can follow. The cost of a poor third side is rarely limited to one box.
Before each move, identify the affected boxes and count their sides. This becomes fast pattern recognition after a few games.
Recognize long chains
In a chain, opening one box makes the next available in sequence. Its value is not just the number of points but also who controls the transition to the next region.
Map connections while safe moves remain. One internal line can join two areas that looked separate and change the entire endgame.
Sometimes give away a few points
Taking every offered box immediately is not always correct. By conceding a few points, you may force the opponent to open the next long chain and gain more overall.
Calculate the forced replies before a controlled sacrifice. It works only when the next region returns more points and the opponent has no safe exit.