Dungeon Mastering is an art form. It is the art not only of telling a story, not only of entertaining your players, but also of giving those players the tools for them to create their own scenes, to affect the world around them, and to truly choose their own adventure. A DM should take pride in an entertaining and memorable session.
Although all players should be contributing equally to the creativity and immersion of the session, It's up to the DM to set the stage and ignite the fires of the imagination. If given the right details and prompts, players imaginations will flare to life and they'll run away with scenes. The DM's job is not to overlord a game session and beat players into the ground with oppressive rules and dialogue. The players don't care about your masterfully written campaign history or how many hours you spend fleshing out every NPC in your world. In the long run none of that will matter. The DM's job is to suggestively and seductively plant creative seeds in the players mind and carefully nurture them to fruition. This means that being a DM is an art. It requires a degree of empathy, the ability to read faces, interpret moods, alter the flow of combat/story to alleviate boredom and inspire immersion.The players will do the rest.
Details should be applied at the players request, or otherwise strategically to inspire curiosity and interaction. There is no need to tell the players every boring detail about your city if all they want to do is find an Inn/Tavern/Brothel/Store. A four paragraph description should not greet the players as they kick down the decaying door sealing the ancient wizard's tomb. A player does not need to know where the stitching pattern of the noble NPC's garment. Conversely no player should ever be left wanting of descriptions and imagination fuel. It's safe to strategically employ key details in scenes and gauge player's interest and reaction to the crumbs you sprinkle. While traveling through the city to find the Inn/Tavern/Brothel/Store there's no harm in mentioning key landmarks they pass en route. It's also a great time to introduce NPC's big or small. I recently introduced "Gorvi the Dungsweeper" as an NPC while the characters were searching for a Apothacary located along the waterfront district. An NPC of zero importance was briefly mentioned and the PC's took an immediate interest in his backstory... of their own free will and without beating them over the head with unwanted details. At the same time several of the main streets were name dropped and a few key buildings were passed... just enough for the players to remember "Oh yea, that theater place is on.. Circus Street? Festival Street? Something like that". It doesn't matter if the details are fuzzy, but it does matter that they are attempting to recall the information because it's being given to them in easy little bite-sized chunks. Knowledge of your setting and the ability to think on your feet are highly prized attributes to possess in order to strike this fine balance.
It was told to me that people think in terms of "scenes" not rounds, or hours, or even days. The more I think about it, the more it makes sense. Ask your players what their characters were doing seven days ago and you'll get answers like "well.. how long ago were we in that dungeon?" or "Well I think it took us about a week to journey through the forest right..?". As I'm sure most players do, mine think in terms of meaningful scenes. Ask them how many "adventures ago" something happened and they'll be much more able to recall the event in question. Enforcing a linear flow of time in a fantasy game is the equivalent of watching paint dry or trying to recall uninteresting pieces of information for a midterm. If the overland travel to a nearby city is uneventful then so be it! There is no need to make players set camp, create a sentry rotation, and re-memorize their spells every day for a four day peaceful journey through The Shire. Looking back on the previous point, and using overland travel as an example, details can still be strategically placed to inspire curiosity. Skipping straight to the third day of travel through a forest, when the PC's stumble past the ancient site of an overgrown fort, is perfectly fine.. in fact preferable. Players get bored easily, and DM's burn out quickly. Skip straight to the good stuff unless it's absolutely necessary for plot reasons.
The world goes on with or without the PC's. More importantly than your knowledge of rules is your familiarity with the world itself. Become intimately familiar with stage that your actors will tell their story upon. PC actions should have reactions. The better you know your setting, the better you can create a truly interactive environment. Don't drive yourself crazy trying to micromanage every NPC in 100 mile radius, but don't be afraid to place bold and conditional new details in the world based on your players decisions. The haunted forest they cleared out? It turns out some of the best wood in the region can be found there. Loggers from the nearby small village have set up a camp thanks to the players. My players recently probed the lair of a juvenile black dragon but didn't fight it. The result was a dragon rampaging across the farmlands the next day and taking out several farmsteads before returning to it's lair. Players have a direct role in the development of the story and the world itself, don't be afraid to explore the possibilities.
DM'ing is a constant learning experience, and I hope to improve my game in order to contribute to the entertainment of the players and myself. No one side should be clearly dominant. Players have an obligation to interact creatively and enthusiastically, but a DM's job is to inspire and facilitate those feelings and desires so that all players can enjoy our time spent together at the table.
What things have you learned to make you a better story teller?