It is possible to skip levels right after clicking start. On your keyboard press 1 to go to level 10, 2 to go to 20, or 3 to go to 30.
The secret levels in Astro Barrier are accessible before level 11 starts. Wait 30 seconds a when the screen is showing information about the orange switch, and shoot the blue ship that appears. Then after the 10 Secret Levels, you will skip levels to level 16.
The Expert Levels are accessible before level 31. Just like the first secret levels wait 25 seconds and shoot to make the turret shoot the blue ship. Then after the 10 Expert Secret Levels, you can shoot five targets with a number of 500. That means you got 2500 extra points. Then the game is won.
You can earn more points to addition to your coins by shooting at targets and torrents when they are in the Instruction Pages.
Before proceeding on to another level, a loading box will appear for about 4 seconds, this box isn't a real loading box, so by pressing enter, it will disappear and you will progress to the next level.
Press the left and right arrow keys to move your ship. Pressing the Space Bar will shoot, but the player has limited bullets, ranging from three to eight.