There is something which almost all Dungeon Masters do when narrating the game, almost as if it is an unwritten rule of role-play storytelling, but something which writers are generally advised against doing. It is called filtering. Eliminating it from prose makes for stronger narrative, increasing the sense of immersion and immediacy. I believe it does the same for a DM's game narration.
What is filtering? Filtering uses unnecessary words which impose an added layer of narrative distance. It reports the perceptions of a character rather than giving the player the sense of perceiving through the character's senses. These unnecessary words are the perception words themselves. I'll give you an example:
1. "You see the wolf snarl and run toward you."
2. "The wolf snarls and runs toward you."
The two sentences are very similar, but the first one uses filtering with the verb "see" while the second does not. Which one is stronger? Which one feels more immediate? The second sentence assumes the character sees what is being described. Why else would the DM be describing it? It is redundant to say "you see." The DM's job is to describe what characters see, hear and feel and it is not necessary to keep reminding them of that fact.
Let's try a longer example:
1. "You see an ancient castle before you, black and crumbled with age. At the top of its highest tower you see the orange flicker of light in the window and hear a ghostly moan drifting on the air. You smell something foul rising from the moat and see movement in the water. You notice strange signs carved into the wooden gate."
I'm pretty sure we can all imagine hearing this around the gaming table, and it sets the scene adequately. But what if we try it without the filters?
2. "An ancient castle, black and crumbled with age, stands before you. Orange light flickers from the window of its highest tower, while ghostly moans drift on the air. A foul smell rises from the moat as something moves in the water. There are strange signs carved into the wooden gate."
Once again, the narrative is stronger and more immediate with the filtering removed. Constant filtering also leads to repetitive sentence structures - another thing that should be avoided in storytelling.
Boxed-text for published adventure modules, the text which DMs are meant to read aloud to players, are usually straightforward descriptions that do not use filtering. This is because it is obvious that what is being described is what is being perceived. This is the way the DMs should narrate.
For some reason, however, DMs tend to gravitate toward a filtered narrative style. Maybe it comes naturally when using second-person narration. Perhaps there is a sense that it actually increases immersion to have that constant reminder that you are hearing, seeing, feeling these fictional things. It really does the opposite, however. Instead of letting players see through their characters' eyes you are having them see over their characters' shoulders. By getting rid of the filtering, by assuming that what is described is what is perceived, then you actually put the players in the role of the character.
As with most writing advice and guidelines, this is not a blanket prohibition. There may be times when filtering is appropriate, especially if you want to emphasize the act of perception:
"Despite the heavy fog, you see the form of a hunched man walking toward you."
Another reason that DMs may use filtering so often is their desire to create a sense of uncertainty in their players. Because magic, illusion, trickery and mystery are common elements in fantasy games, by saying "you see a dragon flying overhead," as opposed to "a dragon flies overhead," a DM may be implying that what is perceived is not necessarily what is actually happening. Some DMs consistently use the filter words "seem" or "appear," as in "you see what appears to be a hunched man walking toward you." This does convey uncertainty, telling players that they should not necessarily trust their initial impressions. It has the effect, however, of dulling whatever reveal is in store. If it is indeed just a hunched man then the set up is unnecessary and if it is something else, then that has already been telegraphed to the players and they will be less surprised. Being in a constant state of uncertainty means players will rarely be surprised by anything. Fantasy requires suspension of disbelief and it is counter-productive to have players actively disbelieving what is being presented to them.
When narrating the scenes of your game, think about how often you use filtering and try to cut it out as much as possible. It will make your storytelling that much better. DMing involves a lot of improvisation. Creating vivid descriptions that draw players into the scene can be challenging, but by making a small change in how you use language you can take your game to a whole new level.