You can earn bonus points by eliminating multiple applians with the same shot. Take your time to line up your shots because of the slow speed at which the applians move. Applians drop down in waves. By waiting a few seconds, you can have them stacking on top of each other to set up large chains that can be eliminated by a single shot. When applians are in close proximity to the shield, a red exclamation mark will appear. Shoot them down during this time to earn "danger" bonus points. You will earn bonus points at the end of a level based ib how much shield power is remaining. Try not to get hit at all to maximize those points.
Shooting
Tap and hold the screen to constantly charge up your shots. If done correctly, you will be able to shoot a fully charged shot at every wave. Use a second finger to curve the shot, then let release it, while keeping the other tap held. You can create a curved shot by moving a second finger in the opposite direction of your first finger to make the shot move in a U-turn and return to Earth. Use this type of shot to get big chains in separate sets of applians.
Vibro-skill
Your sati's vibro-skill charges when applians are eliminated or when your shield takes a hit. Shake your device to activate it. It can sometimes clear the entire screen.