Connect your two sides. Draws are impossible.
Fill cells in turn. Blue connects left to right, red connects top to bottom. Blocking your opponent also builds your own path — that is the strange beauty of it.
Invented in 1942 by the Danish poet and scientist Piet Hein, and independently devised later by Nobel laureate John Nash. It is one of the rare games proven mathematically to never end in a draw.
Use bridges. Two cells a diagonal step apart are effectively connected: block one and you still have the other. Chain bridges instead of laying stones side by side and you will cross the board far faster.
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