At the beginning of a game of Galaga avoid shooting at the ships as they go into their first formation. Then destroy all of the ships except for the yellow/blue ships in the first row from the left. Let the two remaining ships fly and shoot at you for several minutes. Be sure not to fire even one shot until the ships stop shooting at you. Once you're sure they've stopped shooting destroy them. Once you have destroyed these ships you will see that no more ships will fire throughout the rest of the game.