Tips & strategy
An open row of three, one with empty space on both ends, is the key threat. If your opponent ignores it, it becomes an open four, which cannot be stopped because it threatens to complete at either end. Learn to make open threes and to block your opponent's the moment they appear.
The winning weapon is the double threat: one stone that creates two separate ways to make five. Look for placements that extend two lines at once. Your opponent gets only one move to respond, so if you have made two threats, one of them survives.
Do not play passively by only blocking. If you spend every move stopping your opponent, you never build your own threats, and eventually they make a fork you cannot answer. The strongest defence is a counter-threat that forces them to respond to you instead.
Control the centre early. Lines radiate in all directions from central points, so a stone in the middle contributes to far more potential fives than one near an edge. Pushing play toward the sides shrinks your own options.