X-Out

When you are confronted by the first end of level guardian shoot off the 
bottom hooter (the one closest to the skull) then position yourself so that 
you are not shooting the last hooter (the top one). Make sure you are only 
shooting the bubbles that he fires at you. This should give you approximately 
20 credits per second. This takes ages, but if you are persistent leave your 
room for an hour and come back. 

In actual fact you can have twelve different ships. All you do is press 'F1' 
for the first ship fully decked with weapons. Pressing 'F2' for the second 
ship and so on. After a while you won't get any more ships because you will 
run out of money.

The best ship that will last the longest is the last one with the bottom three 
way laser, two non-moving satellites placed either side of the ship. Then get 
the arc satellite, sprite bomb and bouncing bombs. It is also very advisable 
in the later levels to get the shield. 

Choose any of the 4 ships in the shop. Click the ship as usual onto the blue 
print screen and then choose the invincible icon (the one below the laser - 
the one to the right of the orange spiked ball). Now drag this icon to your 
ship and click it on and off the ship. Your money increases by 500 units. Drag 
the icon to the Alien Trash Can and trash it. Carry on doing this to boost 
your money to your heart's content.