Try to place stones on the corners whenever possible. Your opponent cannot outflank these stones.
Avoid placing stones on one of the three neighbor fields of a corner unless you are absolutely sure that your opponent will not be able to put a stone on a corner.
Sometimes it is better to offer some stones to your opponent.
Try to put stones on fields which prevent your opponent from moving.
Try to force your opponent to put a stone in a neighboring field of a corner.