Every 20,000 points you receive an additional fightership. The faster you fly, the less fuel you consume. You receive added points for added speed. If you fly outside the Electron Posts after level 1, you are likely to be hit by Electron Pulsars. You are more vulnerable to attack by Alien Saucers when flying low.
Saucers are more vulnerable as they fly past from behind.
Enemies appear in waves. Try to determine the rhythm of the waves. Over-steering may cause you to collide with Electron Posts, Alien Saucers or Space Hoppers.