Bringing locations, items, and people to life is a big part of tabletop role-playing games. Details are a big part of this and the way we use them can have a big effect. However, there is such a thing as too much detail. As well, there is the question of who gets to create the details. It could be the Dungeon Master, the player, or a collaborative effort. Which details should be focused on? With that in mind, I hope to explore the topic and give some of my thoughts on the subject. I'll use theatre of mind for my examples in order to make the situation obvious. Miniatures add their own power and problems, since it's quite common not to be able to find the perfect miniature for a situation.
Which Details to Focus On?
As with all things, there is a bit of a cost-benefit analysis on the kinds of details we provide. Time we spend describing things is time the players aren't acting. However, we still need to describe something otherwise no game can occur. There are some major approaches I've observed and I hope to give an outline to them.
You can try to describe the things that are immediately important for the thing you are dealing with. The great thing about this approach is that it is simple and keeps things in the players' court. However, it is a minimalistic approach. Taken to its extreme, you may end up describing a sword as merely its stats and location. If it's exactly the same as a previous item you encountered, however, this may be perfectly fine. It's also common to use this for some environmental features.
“The door creaks open. The room is dimly lit by the sunlight coming from the small window set into the wall opposite to your location. The room is full of barrels, leaving barely any space to enter. 5 feet by 10 feet is reachable but you don't know how big the room is due to all the barrels.”
In this kind of situation, even though I provided details, the barrels aren't described. If I embrace this approach, I get something like the below.
“You can see that the room is full of barrels, leaving barely any space to enter. 5 feet by 10 feet is reachable but you don't know how big the room is due to all the barrels.”
It's a little dull as a description. However, this doesn't mean that it's necessarily bad in every circumstance. If your players hit a metaphorical orc bee's nest (a literally orc bee's nest would also work), quick descriptions like this keep the tension going and also reflect the split second decision making process they might use. It can also be made to work by forcing players to perform actions to notice more details or to ask the Dungeon Master if they are curious.
There are a couple of issues with this approach in general use. If you plan to make a detail important, you either have to mention it (cueing your players) or not mention it until they look for it (which can come off as a bit cheap). It's also not the most immersive and interesting description method.
Couple of Details
I usually pick a couple of senses (sight and sound tend to be the most effective), describe what makes sense using those senses, and single out all/most of the important parts of the area/creature/item/thing and describe them. In the previous example, the important details of the area were the light, the amount of space possible to move, and a rough description of how many barrels were tetrised in there.
The important parts take some experience to identify easily but I find the easiest way is to ask questions. If it's a location, what will your players be doing there? Keeping some of the senses in mind helps you make nice immersive descriptions (at least compared to the previous approach) but also means that a detail isn't immediately important. It could just be a touch of character, forcing your players to do some thinking and extra searching. It may also make sense that your players cannot see an important detail because of some obstruction or features of the location.
Sometimes, you want something awesome to make an unforgettable entrance. In these cases, the description becomes very important. However, since an entrance is usually done by something sentient, we have to also typically describe actions. This forces more time to be spent since time also now plays a role.
If it's a dragon, you'd typically describe everything in the above section to fill out the appearance, and also need to describe its actions (how does it walk/fly in and does it say anything?). We might sometimes want to trim down some of the description and instead focus on actions. It will probably take more actions later and if you really need to, you can give a couple more details then quickly.
Details Not Covered
You typically only have a few words to get across a description, so you need to use them wisely. This means that in some situations not everything will be said (though visual aids can greatly help to save on words and get more information out more efficiently and interestingly). What happens in this situation? The obvious answer is that in the future, when it makes sense, the other details will be revealed because the Dungeon Master knows. Maybe when the player comes closer. Maybe when the player tries to actively look. Or maybe just after a moment in the room they'll notice something. There is another option, however, though I've seen it used more often for items.
There is a bit of a power dynamic between a Dungeon Master and their players. However, this power dynamic isn't necessarily the same between different groups. Say, for example, that the players beat some undead humanoid and take its magic weapon. Before leaving, they cast Speak with Dead and learned something about it. You could come up with the entire back story for the item. However, you could also give your players the chance to come up with its story as long as it relates somehow to the character they killed. If they ask 5 questions, you might even let your players answer some of them. This still keeps the collaborative storytelling that is the heart of tabletop RPGs but also results in them contributing to stories they otherwise would not have. It also drives a bigger wedge between the player and their character. The simplest examples is to let your player name a magic item they found and then construct a past (they get a name they like and you still have control). The more complex is to temporarily give your players the reigns over your part of the game. This topic is what I'll be covering next.