To activate the cheat mode type "Zvmo!EG" as a password. Type exactly as shown.
The most important thing to remember is that all the puzzles can be solved without losing a life, so if you lose a life and think its the only way to solve the screen, look closely. Some of the puzzles get pretty obscure after level 10, but once you eventually beat them you'll kick yourself for not seeing the solution earlier.
Look before you leap. Think about how the screen will look from a flipped perspective. A lot of jumps you make will be unnecessary and waste time and switches if you don't.
Make sure you have enough switches, at least 10 per screen. It is possible to get stuck on a downward slope with no way to get back up or kill yourself, and the only way out is to press 'ESC' and start the whole game over.