While you are adventuring, find a treasure chest and make sure you have a key. Hold down 'INSERT' while you open the chest. Release 'INSERT' and hold the joystick down. Now pressing 'HELP' will give you 5000 health points.
When you open a treasure chest hold down the 'HELP' key, then when you open a second chest hold down the 'INSERT' key. A golden cross should appear, collect this and your health points should rise to 50,000. You will also have 32,000 super shots for the remainder of the level. The shots will vanish once you leave the level, and if you pick up an amulet, the counter will be reset to 10 shots.
To avoid tricky levels, pause the game and wait for three minutes. Press 'fire' and all the walls turn to exits. This happens anyway, but if you pause the game, you don't lose energy, and won't get attacked while waiting three minutes.
To get into the secret room, clear the dungeon completely, picking up the super shots last, then go to the exit without pressing 'FIRE'.