Shooting a yellow ship on stage 1 : 80 points.
Shooting a blue ship on stage 1 : 80 points.
Shooting a falling blue ship on stage 1 : 100 - 800 points.
Shooting a bird dead center on stage 2: 100 points.
Shooting a bird's wing on stage 2 : 20 points.
Docking the ship on stage 3 : points awarded for remaining fuel.
Shooting the falling ships on stage 4 : 100 points.
Destroying the mother-ship : 800 points.
TIPS AND TRICKS
On stage 1, you can ignore as many yellow ships as possible, and only aim for the blue ones. When the yellow ones move off screen there is often a chance that the next wave will include a blue ship. Since the blue ships are worth more points they are worth waiting for.
On stage 2 the birds do not fire until they are fully developed. You can usually take out 3 or 4 of them before they start firing.
On stage 2 you can concentrate on continual fire on birds wings when there are only 2 or 3 remaining, as this awards 20 points per hit and does not destroy the bird. You can rack up a good score by doing this, but watch out for the falling bullets.
The asteroids positioning on the docking stage is totally random, so this stage is often down to chance. Do not use your thrusters to maximize your bonus points.
On stage 4, the ships which come down from the cloud move across you from left to right and back again. You can time your firing so that they are hit when directly above you. Note that only the mother-ship fires at you so you can take out the ships when not directly below the cloud, and be safe in the knowledge that you have no bullets to avoid.