Valve Software, makers of the Half-Life series of action games, recently released a very strange little puzzle game called "Portal." If you're unfamiliar with it, I recommend you watch the trailer, because it does a much better job of explaining the game than I could with words.

One of the nice things about this game is that it comes with developer commentary that you can listen to as you play the game, which gives some insight to their design process.

Perhaps the most interesting thing they discussed was that they treated almost the entire game as a tutorial. Which isn't to say that they hold your hand the entire game (quite the opposite!), but rather that whenever they weren't teaching you new gameplay tricks, they were reinforcing the old ones they'd already taught you. They found that if they didn't, players would routinely forget that the old moves were still options.

If that kind of design is necessary for a game that only has one basic mechanic (the portal gun), then it's doubly important for alternate reality games, where the players have almost total freedom. It's so much freedom, in fact, they may never realize what it is you're trying to get them to do.

For example, if you have a character who has information that the players need, but won't reveal it unless the players ask him, then make sure you cement that character as a source of information beforehand. Have the players ask him about several other things prior to the critical moment. Even if the early questions are a little meaningless, the act of asking is important, because it lets the players know that that is what you do with that character.

But, as the Portal designers mention, don't try to reinforce old ideas at the same time you introduce big new ones, or the players will become confused and frustrated. Show how the new mechanic works, then show how it fits with the rest of the game. Those two steps can happen very quickly, though.

To sum up:

1. Tell your players what their abilities are (one at a time).
2. Whenever you're not doing that, remind your players of the abilities you've already shown them.
3. This process can (and in some cases should) last an entire game.

Portal is a fantastic game, and it's nice to see the process used to make it explained. By applying some of their ideas to your game, you can help make your game as tightly designed as theirs.