GM RULE #1: Always say, "Yes, but . . ."
It may have been said before, but GMing is an artform that is ever-evolving. My formative years of gaming had GMs with the mindset of GM vs. Players. I have seen a lot of players that bring that attitude with them to my table. To me this is a crazy, incongruous concept, as the GM dictates the world around the players. My style has always been that gaming is a cooperative experience with the GM being more of a program manager, or director on a movie set, or even a facilitator. The universe revolves around the players' actions, no matter how small or large the scope of the game. This could be used for an adventure as mundane as a group of Shadowrunners (Shadowrun is one of the greatest games ever created -- both the tabletop and PC versions.) going to the local grocery store for beer, or something as epic as Elric determining the fate of the world with his choice of Law or Chaos.
When asked a question from my players, the answer is "yes" 98% of the time or "yes, but . . ." All actions are open to my players, and I explain to them that while they have all of this amazing freedom, all actions have consequences, some of which may not be visible right away (particularly for campaigns). This type of approach usually leads to some of the greatest RPG moments and requires a lot of thinking by the players to manage. Most players nod quickly and take advantage of the freedom given to them, but that enthusiasm for freedom quickly subsides when the consequences rear their usually-ugly head(s) to thwart them. My poor Scion game was the worst case of always-saying-"yes" going horribly wrong because the players did not grasp the concept of consequences (a more detailed post for another Friday).
Saying "yes" creates story, which is the core of any RPG. It also creates a safe space for players to express their ideas and helps bring out shy players that primarily sit in the back and surf along.
An example...
A few years ago, a group of players were playing through Dawn of Defiance using the SAGA edition. (Possible spoilers ahead for Star Wars SAGA Edition campaign.) This campaign takes place during my favorite time for Star Wars: The Dark Times. It is just after the Jedi Purge, The Rise of The Empire, and you have nearly everything still in play. Beautiful. It is a time when choosing to be a hero means going up against impossible odds and each minor victory is in and of itself a miracle to be celebrated.
The Heroes
Toleph-Sur Turai (Human Scoundrel): Street orphan-turned-actor who masqueraded his way into becoming a Pirate Captain until ousted by the crew. At the start of game, he is looking for a new ship and crew.
Cad Vookto (Duro Scoundrel): Ace pilot without a ship that loves his home world and hates what the Neimoidians and the Empire have done to it.
Jento Fett (Clone Trooper): Jento doesn't know why his switch did not activate and is still loyal to the Jedi. He will topple the empire and give his brothers back their free will.
McKenna Castle (Human Jedi): She escaped the great purge and has re-assumed her roll as a diplomat while aiding the Rebellion. She knows it is only a matter of time before she is discovered.
Lothrakka (Wookiee Scout): A recently escaped slave who wants to destroy the empire. He can't do it alone and is looking for allies. He plans to free every slave he can.
The Story
The party had fared well for their first few sessions but had reached the imperial base on Felucia and tripped the alarm. The group found themselves overwhelmed by wave-after-wave of stormtroopers, and eventually Toleph, his blaster having run out of shots, gave his team an impassioned speech about freedom, that if they die it is for the right cause and the pirate life. He scored an amazingly high roll (coupled with some impressive roleplaying) that left the junior Imperial officers stunned for a round. The unfazed stormtroopers continued firing and flooding the room. Seeing the stunned officers, Toleph's fellow players asked if he could spend a Destiny Point to have one of the officers close the blast doors. Following my golden rule, the answer was yes but you need to roleplay it out.
Toleph dodged through an array of blaster fire, rolled up to a young Lt. Kraine (three weeks out of the academy), gave her a few moving words about the Rebellion, and kissed the officer. What the player did not expect to happen was for the officer to permanently change sides and become his sidekick/lover for a number of sessions until she was killed saving his life.
That simple "yes" brought a RPG goldmine of complications and rewards all at once. It created tension, having a "former" imperial running around with the party and also gave the party low level Imperial Intel (if it was truthful). Lastly, it changed the way Toleph experienced the game and established an ongoing tragic romance element to his character. That was not the last lover he found and lost.
That's the power of always saying: "Yes, but . . ."