“Show me, don’t tell me.” It’s some of the best advice I ever received when I was taking creative writing courses. This is a way of letting the reader draw their own conclusion about what’s happening rather than the storyteller hitting them over the head with blunt and direct descriptive terms. It’s good advice for writers and it’s good advice for DMs.
The best DMs I’ve played with are masters of “show me, don’t tell me” even if they don’t realize that they’re doing it. The key is in the details. When you’re trying to convey emotion don’t just say “The man was sad,” describe the character and the body language and let the players draw their own determination of the NPC’s mood. “Although most people think the man at the next table is passed out, you can just make out the sounds of soft whimpering and sniffing as tears no doubt rolled down his hidden face.”
Describing the scene in this way requires a lot of little details. It takes longer to write and longer to read. You need to decided when it’s worth slowing things down to add these details and when it’s better to just tell it like it is. There’s no hard and fast rule, it’s something that comes with practice and experience.