If you want to improve your performance as a DM, understand how to tell a joke.
A joke is the opposite of improvisation. The pieces and parts of a joke are designed to be told in a certain order, with exact words, with the right amount of emphasis on each word so as to set up the joke without giving it away. The pacing must be arranged so that the joke's delivery adjusts its speed in the telling. To tell the joke just so, it should sound sincere, even if you've told the same joke a hundred times.
There are too many who don't understand what they're doing when they tell a joke. They speak with the same flat tone throughout, they forget details, and then try to insert them out of order. They give away the punchline by including the critical innuendo in the telling instead of waiting for the end; and they give the punchline with far too much expectation in their voice. With such people, we give a half-hearted acknowledgement, perhaps a polite laugh ... and inwardly roll our eyes when this encourages them to tell another joke.
Describing a dungeon room, or an non-player character, or laying out the details of an adventure must follow the same rules. Know what you're going to say and in what order. Adjust the tone of your voice to emphasize important things ... but don't assign them too much importance with your voice, or you'll lead the players straight to the answer. Don't forget details and try to insert them after; this ruins the scene as well. Maintain a degree of detachment, conveying your indifference to what they investigate, but paint the scene and events with enough emotion that the players aren't sleeping in their seats.
This is not as easy as it looks. Neither is telling a joke well. Find a joke you like and practice it. Explore the different nuances and strengths of the joke; think about why each word in the joke has been chosen from among a thesaurus of other, similar words. Figure out what you think is funny about the joke and then dwell on that. Remember, jokes are not intellectual, they're empathic. If you don't feel the joke, it's a dead fish.
You'll know when you've told the joke well when you find you're enjoying the joke yourself ~ not because of the laughter you hope it produces, but just because you really like the joke, and it feels good in your mouth and your head as you deliver it. Strange to say, but you may learn that the best part of the joke is not the punchline.
Which reminds me ... this student gets a job with a farmer for the summer, and one day when he's sitting at the dinner table with the farmer's family, this pig comes in ...