Lightsaber power-up will slice cleanly through any enemies it comes into contact with but there's a light pause between picking this item up and actually using it.
Always keep your ship moving around the screen in a circular fashion, with the enemies clustering nearby to you.
Do not try to kill anything that isn't a dot using the floating power orbs - they won't have any effect at all.
The value of enemy dots increases as you kill them overall, so the longer you can last in the game, the greater opportunities you have for achieving a high score.