When starting a new game, concentrate only on the missile to save money. The missile is usually the best option. It takes down all comets and earns the most coins. The cannon is the next best choice if you are not strong enough to destroy the comets with other weapons. It provides a chance for them to drop items before they explode. The laser is only useful when you get a lot of packed comets, however the missile can also handle that task. To take down comets, shoot missiles at regular intervals at the left side of the screen. As soon as a comet enters the right side, the missiles will home towards it, giving you a few extra hits.