A Trick : You can determine which direction the end of level boss will move before it even appears by looking at your score. If the hundreds digit is odd, the boss will move to the left. If it is even, it'll move right (the tens and units digits are always zero).
One Million Points Bonus : On the violet continent, if you see a coelacanth fossil on the left side, go to the -right- side and shoot. Cleopatra appears - shoot her and you'll get a million-point bonus. The coelacanth may only appear on the third violet continent.
80,000 Points Bonus : At some points in the game you will see two columns of green arrows down the center of the screen. Concentrate on either the left or right column of these arrows, and try to shoot 16 in a row. You will be awarded an 80,000 bonus for doing this. The first time these appear, it is possible to get two such bonuses in a row (if there are not many enemies around!), and sometimes more if the level ends before the column has finished appearing. Later on there is a short column of only 16, so only one bonus is possible here.
50,000 Point Bonus : You've seen a big enemy that combines into parts. When you hear the tune it is about to appear, STOP SHOOTING (You don't actually have to stop shooting altogether, but if you hit part of the enemy before the center part flashes white the bonus will not work). Position your ship so that you are just underneath the center part of the enemy and wait for it to flash white. Once this has happened, shoot the center part several times : the enemy will be destroyed and you will be awarded the 50,000 point special bonus.