Catching Enemies: It's important to learn the enemy patterns. Once you know how an alien will react, you can target where he will be rather than always trying to catch him. You can also wrap around the screen and get them from the other side.
Avoiding Missiles & Plazma: The Rambo approach will not work in this game, nor can enemy shots be destroyed. Just make sure they are off the screen and you'll be fine.
Asteroids: It's much easier to wait for an asteroid to appear on screen and go after it as soon as you see it. DO NOT try to blast a 'roid if it is just barely on the screen! You'll never catch it in time. Let it go. Some 'roids you must shoot twice to destroy. Therefore, it's safer to shoot every 'roid twice just to be safe.
Hull Strength: Avoid getting hit in the easy Sectors. You'll need to save up energy for the harder levels. You get about 1/4 of your hull strength back when completing a Sector, so don't fall below that, and you'll max out your strength for each level.
|As long as the plazma balls are off the screen, they can't hurt you.||
Don't chase the asteroids. Wait for them to you instead.