Dipping a ladle into our suggestion pot, I see that NinjaBait had a question  about setting details:
I’ve been a DM/GM for several years now. I’ve never had any complaints about my stories or settings, but I’ve never felt very comfortable with describing what I’m seeing in my head. “The pungent stench of mildew emanates from the wet dungeons walls as stagnant water sloshes around your feet” becomes “you’re in a sewer and standing in about a foot of water”. How can I improve my ability to frame scenes without spending time writing out each one before hand?
If your players are enjoying the game, you’re probably hitting the right notes. That said, we all like to grow and improve (even to Medium size without a pesky enlarge person), so let’s discuss a few handy techniques.
Ah, the dreaded “box text”. When you’re running an adventure, the writer often crafts an evocative image–if your players have the patience to wait. The balance here is tricky; players usually wait just long enough to get a good image in their mind, but they’re mine usually act instead of waiting to hear how thick the tomes on the shelves are.
While this isn’t the solution you’re looking for (pre-writing is something that comes from modules more than home campaigns), you can still suss out your players’ tolerance for description by imitating different writers’ styles. It often depends on the moment–I know that I’ll listen to wallpaper being described to set a spooky scene, but if there are opponents and weapons, I react to the obvious threat. In danger, more than a sentence or two of description seems out of place–my character’s worried about the quarrels zipping his way, not the teak panels behind the orcs.
If you want to read a fun debate about box text, Walt’s article and comments  feature interesting takes. Heather at Errant Dreams had a good article about making use of detail  that might help you narrow in on appropriate levels of description.
If you have the right image in hand, a picture IS worth a thousand words. John had a great article  about sharing the book’s artwork to get everyone on the same page. Similarly, in my wife’s campaign, she found 6-8 images from the web for key elements (monsters, ravines, etc.) in the upcoming night’s adventure. She’d save them as a slide show, advance to the proper slide, and turn the screen to face us. It was very cool to see the chasm–you could see the river glinting below; creepy pictures of half-rotted corpses shambling through the swamp set the scene very effectively. They weren’t generic zombies after we had an image to fix in our minds.
John also has a good article about using–and improvising props . As a GM, I tend to be less prop intensive, but I know that I’m very impressed as a player when a GM pulls out a scale model of the ship, or the sewers we’re trekking through.
Sound files can make excellent props. You can play the sound of a waterfall, drawing everyone more completely into a scene, instead of just describing the rush of water. Some sound effects for gaming were produced by World of Twilights , who volunteered the prizes for Gnome Stew’s first contest  a few years ago.
Your instinct, to visualize the scene then describe it, is excellent. If you never thought about how a room looks, you’ll never see the details and describe them in a way that makes them come to life. (I don’t know how many adventures I went through with tapestries, when I’d only ever seen them in a textbook. Once I saw some real life tapestries, I had a much better sense of their feel and impressive presence. That’s hard to capture with a 3″ high picture.)
Troy’s article about getting in touch with your wild side  reminds you to get out and explore in real life. It’s much easier to describe the creepy slickness of the cavern wall when you recently visited a cave, or the susurration of grasses as the breeze gusts across the plains, when you’ve got a great mental image to call up.
For my prep, notes and reminders are where I concentrate my efforts. Matthew has a great location template  that reminds you to include key elements when you prep a new location. Note that “ambiance” is the second element that he lists; a few key words or phrases (the whoo of an owl, the erratic splatter of rain as the wind gusts from west to south and back) can help you convert your mental image into a vivid description come game time.
Similarly, locations in FATE games have aspects–key elements–that can be brought into effect by both sides. Boiling a location down to three or four aspects is enough for a solid feel, without tying your hands to box text. For my 1930s game, I had the following aspects for Campeche in the Yucatan: Bustling, thriving market; Oppressively warm; Jungle crowds close. Having those aspects on a 3×5 card before me guided me in setting flexible scenes across the city, while ensuring that the city had a coherent feel. If they had stayed in town longer, districts and neighborhoods would have received similar treatments, but because the game was an Indiana Jones style globetrotting game, broad strokes illustrating the differences between locations worked best.
3×5 cards are a great solution. You can either make them general–something you refer to each time you describe something, or specific but random–a list of specific prompts and ideas that you build a deck of and draw when a new situation develops.
Example of “general solution 3×5 card” (probably pinned inside your GM’s screen):
-Smell and Ambient Sound
Conversely, a deck of specific prompts might include the following cards:
-Gnaws on hardtack while others talk
-Reeks of something dead
-Cape sweeps up and tugs at his neck in the stiff breeze
A general card prompts you to describe specific things–whatever you don’t regularly remember to describe in the heat of the moment–like smells. Specific cards give you random prompts, forcing you to improvise, but providing you a prompt so you’re not starting with a blank page. Why does the nobleman reek like something dead? How will the stiff breeze affect the torches everyone’s depending on to navigate the moonless night?
Building a deck of specific images, scents, and sounds lets you take advantage of inspiration between sessions. It can balloon quickly–jotted notes can be transferred and added to the deck. Similarly, if you have two or three things that you’re working on, and you want them to show up until you make a good habit of working them in, you can create two or three color coded decks (smell, action, etc.) and draw a card from each, working them into the scene whenever possible.
How do you craft evocative scenes?
What tricks are in your arsenal to create vivid scenes? Do you write descriptions beforehand, crafting perfect sentences with the time between sessions? Do a few keywords prompt an entire image for you? Or do you have a template of your own that you use to create consistent scenes, drawing on all the senses? Please share your tips and tricks in comments.