Let's learn how to slay the Quantum Ogre.
How do we give players agency—how do we let their choices have the effects that relate to the intents of that choice? The primary rule is stay true to your role as arbiter and facilitator of player choice.
This is the key to player agency, since it informs their choice. Without information, they cannot make a choice with intent. This is important in many ways, in many situations. You must study this.
- When dropping hints, drop them three times.
- When the players are discussing things, and they have misunderstood something or your intent, correct them.
- When the players tell you what they are doing, also ask them what they want (why they are doing it) and make sure that their choice matches their goal. Pacing is difficult enough to maintain—if the players want to find treasure, let them know before they search an abandoned building for six hours of play time that there's not much treasure there. Tell them where to go to get the gameplay they want. (Yes, but. . .)
- Let them know the stakes. Make sure you are honest with them about the consequences, even if the non-player character's are lying to them!* (What's in it for me. . .)
- If you told them, and more than 30 seconds have passed, you may tell them again. (Remember. . . )
- If the players ask a question, try to answer what they want to know. (No, but. . .)
- When dealing with authentic hidden information (how a trick or trap works), give them some sign of all irrevocable effects (Trick/Trap agency)
- Don't give the players blind choices. Always give some sort of information with the choice. A choice with no information to distinguish between the options isn't any sort of choice at all.
This is a sword to player agency, since it empowers their choice. Without freedom, they are unable to make a choice with effects relating to their intent. This is critical since without choice, there is no game. (i.e. games are collections of interesting choices).
- The outcome of a situation in play should never be predetermined—one cannot decide ahead of time how the choice a player makes will play out, otherwise the player has no input and is therefore not engaged.
- Allow things to happen that have no bearing on the players or their interests. If everything in the world revolves around the players, how can they be free? More to the point, how can they ever see the effects (or lack thereof) without a living breathing world?
- One cannot dictate the actions of the player characters! Their control over their characters is sacrosanct territory, with only rare exceptions (magical control etc.)
- The freedom to ignore your plot hooks/adventure thread/situation is critical. Next time you play, look around you—those are actual human beings, not fleshy shells destined to act out what happens next in your fantasy. If they enter your rioting city, and decide to leave, let them get the hell out of there if they wish. . . just remember to let them experience the consequences of their agency.
- The invisible wall is anathema. Say Yes. . . or Say Yes, But. . . If you tell the players they can do anything and then continue to tell them no and no and no, well, they can't really do anything, can they?
- This is ironic, but in order to encourage freedom, you have to limit options. You have to say, here are five tasks, so they can make a meaningful choice between the five—or reject them and forge their own. If you were to tell them "do anything you want" the excessive freedom limits their agency by making their choices meaningless.
 I blame America and its obsession with freedom on this dishonesty. The fact is, you can't do anything you want, and not only is it so important for us to believe we can that we constantly tell ourselves and our children that, but it causes massive social dysfunction (a lack of concern about behavior on community) and personal distress when faced with this reality.
Edit: The publication date was changed for appropriate tag display. The original publication date was 9/12/11