One of the oldest follies of tabletop RPGs is when the DM doesn't know the answer. We discussed how a situation like this can come up in my last article, and now I'll provide some tips to DMs and Players for when the playing halts and how to avoid it.

1. The DM should always be prepared for the most violent response - All too often the DM has some misconception that their players will realize that the shiny-armored NPC in the back is a Paladin with about 5 more levels than them. In reality, they will notice that the shiny-armored NPC not only has some loot but is trying to control them. Furthermore, the stereotypical roleplayer that refuses to metagame is also offended by the paladin in his way for obstructing his in-character goals. All of this combined leads to violence more of than not. Never get caught with your pants down when the PCs attack their arresting officers or condescending dukes.
2. It is OK for the players to not constantly attempt to derail the plot - I know that it's a smug feeling when you pull some crazy nonsense that totally throws the DM for a loop. Usually, in combat, that's OK, but just be aware of when the DM is starting to get lost when you start throwing out truely erratic directions. Don't abandon the story to wander out into the forest for EXP. Maneuver the storyline however you want, but for everyone's sake stick to it.
3. Plan one encounter further than you expect the PCs to get - It's happened to all of us, when we simply run out of adventure because we didn't get this far. We expected Krognar to go down to the Manticore but two lucky crits and the party strongarmed their way through a tense aerial battle in minutes. Now, the rest of the session finishes and everyone goes home early. By keeping ahead of the game a little bit the action can progress smoothly.
4. Do not try to rob the magic shop - All too often certain players forget that in addition to being an immersive world, Dungeons and Dragons is an RPG. It does not make sense that the PCs are the only ones capable of stopping Lord Arch-Nemesis when there's clearly someone conveniently there to sell them Greater Rods of Metamagic. These shops exist because the players need somewhere to spend their gold. Gold becomes worthless if the players are so powerful magic shops (or wherever you go at 17th level for your loot) don't sell anything they don't already have. This is an example of a metagame structure that you are not allowed to abuse as a player because it ruins the flow of the game.
5. Do not let the players try to rob the magic shop - Yes, I know. Every magic shop is owned by a 21st level lich wizard. But by letting them try you're either killing them (bad plan) or pulling a 21st level lich wizard on their ass (not fun). Just firmly tell them that attempting to abuse the immersive world is a bad idea.