Kill the baddies and try not to miss

For every 10 enemies you hit without missing you are awarded a power up, you need to collect 15 of each to reach full power, at this point you still gain extra score for each power up. Extra lives are available when you reach a certain score.

Extra Shot
Increases your shot count up to the maximum of 20 shots, this is the most important powerup if you are using the Twin Shot, as each shot takes up two energy beams.
Shot Speed
Increase your automatic fire rate. You start with a poor 120 shots per minute, but you can tap the fire button to shoot at a faster rate until you power up your shot speed. Shot speed has no effect of the Laser Beam weapon.
Extra Power
With more power your shots will not only do more damage but will also pass right through the weaker enemys.
Extra Life
Gives you an extra drone ship to battle the enemy XEN.