Easy strategy to beat the game:
Choose one direction and keep pressing that arrow key with the right duration and interval to stay out of the center. Don't alternate with the other direction, because then you'll gain momentum and get too far away. Make small movements in other directions as necessary to hit threats or get powerups.
Powerups seem to remain indefinitely, so only get them when you need them.
I only got hit two or three times throughout levels 5-10 with this method.