As you might have guessed from the “Boxed Text” segment I’m running, I write boxed text this when I’m really motivated in my planning.
During a game, I’m going to be focused on the players, thinking fast in response to their questions. I’m not going to have full access to my vocabulary, and I’m not going to be able to envision the game world in all of its sights, smells, sensations, and emotional resonance. Those things take time, and (as an introvert) they don’t easily happen while I’m being social.
GM prep is the perfect time for this. When you’re planning a scene, stop for a moment to imagine yourself immersed in it. Feel the crisp breeze, see the bright oranges and reds of autumn in the forest, hear the babbling water of the creek and the crunch of the snow, smell the butter and yeast from the tavern’s bread. (I admit, writing this out, I’m a bit of a hack that goes back to the same imagery over and over.)
Write down the imagery. Even if you don’t read it to the players directly, you’ll remember some of the words you used, and they’ll show up in your descriptions. Think about the imagery you’ve written down, and see if it leads you to other imagery—the crackling fire that you imagined in the old hearth probably casts orange light on the opposite walls and gives off an inviting warmth.
You can do this for NPCs as well. Imagine some of the questions your players might ask (or categories of questions) and write important pieces of dialogue that they would respond with. You don’t have to (and shouldn’t) write out entire conversations, but when it comes to secrets and clues, you want to make sure players get the right impression from your words (and that you don’t reveal something you don’t intend). A bulleted lists of sentences they might say in the conversation is all you need—and will serve you better than a vague idea of what you want them to express.
This also allows you to think about unique words or phrases your NPCs might use, or interesting ways of speaking. Are their revelations short and sweet? Or do they speak at a strange or archaic pace? Are they smirking when they reveal a bit of information?
By planning it out beforehand, you have references you can use for improv, just in case you get overwhelmed with responding to players at the table.