When designing levels, keep in mind you will not be allowed to play your levels until there is room for a player to start and no portion of the level is blocked off. If you save a level in either of these states it will be skipped over. Master the 180-degree turn. This can be done by pressing two arrow keys quickly so Sammy turns around in exactly two frames of game animation. It's not overly difficult to do, and will prove useful in many places.
Timing is the most important skill in the game.
Know when to turn. Also, listen to what the game tells you when you enter a number that is not a valid cheat. Keeping this in mind, I'd like to begin by talking about our weird lives.