You can also encourage everyone at the table to follow guidelines established by improv practitioners; these become less "rules of the game" and more "rules of play" (i.e. they don't really answer "what can I do next" as much as they address "whatever I'm going to do next, how do I do it?"):
Accept every offer. During the course of play, other players will make suggestions about the ongoing narrative, sometimes directly involving your character. Accept what's offered; don't block their suggestions. Try, as much as possible not to say "no", literally, or figuratively. Don't say "no", say "yes".
Accept and build with new offers. During the course of player, when you have an opportunity for agreement, don't just agree (see first guideline). Take what's offered, and build on it with a return offer. There are two ways to do this: add detail, and add complication. Note that both of these help you steer around the natural reaction against the first guideline ("I don't want that!") to "get what you want" or "avoid what you don't want" for your character. Don't just say "yes", say "yes, and..." or "yes, but...".
Make simple offers. There are a bunch of other players at the table; just as with boardgames, play rolls along more smoothly when there's as little down-time as possible. Engaging the other players is key, so when you provide details, be simple, straightforward, and incremental and then throw the tempo to another player (or the referee). When you say "yes, and..." (or "yes, but...") say only one thing.
These are also commonly known as "No Blocking", "No Wimping", and "No Steamrolling".
For some more explanation about how these things work in improvisational theatre, check out the Improv 101 series of blog posts (I found them by googling "no blocking no wimping", so they were a fast find, not necessarily "the best" find -- lots of other improv resources exist). There are lots of ways in which improv doesn't map well to RPG gaming, but in a lot of ways, good advice there is good advice here.
Based on personal experience, I might suggest one that's gaming specific and in the spirit of the improv guidelines:
The game is a player. You can think of the game's rule engine itself as a player at the table: so, when it has offers (i.e. you use the rules to help adjudicate an outcome), don't block or wimp or steamroll its offers. As much as you possibly can, resist temptation to fudge the offers of the game itself; as much as you possibly can, try to play the game as written (before you decide some part of it is "clearly broken" or "not to your taste"). In Burning Wheel, terms, you can think of this as "Say yes, and roll the dice..." The dice can suck, but you must give them that freedom: it makes for memorable play experience.