An excellent breakdown of the brilliant level design of Super Mario Bros. World 1-1, which teaches players almost every crucial rule for the game within the first two frames:

“the big question of level design – and i mean that every level design lesson i ever write will be a response to this question – is: how do i teach the player these rules? an unfortunate trend in contemporary games is to spell out every detail in a hand-holding “tutorial” session at the outset of a game – unfortunate because it shows both a great deal of contempt for the player’s intuition and a lack of confidence in the designer’s own design. but more than that, it’s a design failure because it tells the player the rules instead of allowing her to learn them.

what if the first level of the game were laid out in such a way that the player could learn the rules simply by playing through it, without needing to be told them outright?”

Check out the whole essay, by Auntie Pixelante (via the Wayback Machine, since her site is now defunct).