1) Keep details about where the PC’s are alive and fresh. Set stages. Describe sounds, smells, textures, etc. Keeping a comfortable, full detail level, if done with finesse, will bring alive even an empty dungeon room. It also prevents players from (if you use too much detail) thinking a room is suddenly something special. If your players don’t “feel like they are there” then much of what role-playing is, is lost.
2) Bring NPC’s alive: voices, motives, quirks, and background. With inspirations from movies, books, and even relatives, it really only takes a second to develop “The Barkeep” from a cardboard cutout to a believable character in your world, like the NPC existed before the players and will go on afterwards.
3) Know the immediate world area in which your player’s characters dwell. Rivers, nobles, mountains, outlaws, etc. Keep the world flowing and changing around them so they don’t feel as if the world exists solely for their benefit. It spurs their imaginations in creating a more colorful image for themselves. The more real the game world is to you, the more real it will be to the players.
4) Be alert, responsive, and well-timed behind those screens. Pacing and timing are very important to keeping your game fresh and players excited and enthused. If things drag, turn up the heat, if things are going at a breakneck pace, give the PC’s a small rest. Don’t overpower the PC’s, but give them just enough time to react and make decisions without discussing it like a committee, especially during combat. Listen carefully to the players as they talk, they are possibly the greatest source for ideas.
5) Don’t just know the game system, be one with it. Don’t let rules dictate to you but do not bend them without cause. Know the system so when situations come up they don’t deal with, YOU CAN. Know the dynamics of the game’s mechanics to judge fairly, consistently, and positively to the story.
6) Use your tools well. Use your time well. What good is a long, detailed history if it never gets integrated into your campaign? What good is an adventure you spend two weeks writing if no players are interested in it? Better to take published material and mold it to your player’s characters wants and desires! If you do create a rich and detailed history, use it in the game! Tie magical items, ruins, towns, cities, even the very landscape to your world’s history to give it depth and appeal. Use foreshadowing to enhance storytelling.
7) Don’t humiliate your players or their heroes. Give the player who doesn’t know all the rules some slack. Make sure to involve everyone at the table, quiet or loud. Don’t send the characters traipsing through mud grime and filth for no reason to the story. Don’t beat the characters relentlessly with combat after stupid combat with no resolve. This can all be wrapped up in one phrase: Just because you hold so much power in the game, if you abuse it, you won’t have any players left. The players have come to play heroes. Let them accomplish that with dignity. It’s NOT “you against the players”.
8) Be flexible with character decisions. You already know not to say “you can’t go there because I haven’t made it up yet”, but this extends elsewhere. Be prepared to allow the players free will, or at least the illusion thereof. Be ready to improvise. Reading novels or game books can help you store ideas in your head for that time the PC’s go ‘off the beaten path’, and they will love you for it to allow them to explore the dynamic world at their feet, not your decree!
9) Decide on the flavor of your game and do the best you can to stay consistent with that theme, be it epic struggle, slightly comedic or light, or the medieval tapestry that hangs in the backdrop over the adventure. Use the flavor in your mannerisms, NPC’s, descriptions and adventures to make the world real and involved so the players and their characters never forget where they are.
10) Don’t allow players who don’t get along or mix well with your group or cause trouble to stay. Life is too short, and too many are depending on you to run a good game. Trouble players must GO.
11) Don’t waste time in the game. Don’t allow players to question every decision and rule at the table. Don’t waste time using careless mechanics. How often are you at a table where the DM spends about 5 minutes or more collecting ‘spot’ rolls (or whatever) from every member of the party only to then announce what it is they ALL see. Why call for dice rolls? In a group of five or six characters how often, really, are they ALL going to miss? Have the roll be for surprise, or something. You just wasted valuable game time with a predictable result. Save spot checks for smaller groups or when someone’s specifically searching for something!
12) The ‘funniest’ but most literal advice: WATCH and LEARN from the movie ‘Predator’ starring Arnold Schwarzenegger. I know you’ve seen it. See it again. Don’t just watch it, absorb it’s technique. Mood, setting, description, action, PACING, character interactions, NPC reaction. A perfect blend of a storytelling twist, fast and hard-hitting combat scenes without taking the entire movie, ambiance description, and more. Even if you don’t play sci-fi, watch Predator. I can’t recommend it highly enough when you want to improve your technique and learn how to pace a game that’s supposed to keep everyone excited.